Sushil Kuner, financial services lawyer at Gowling WLG, says:

The FCA is right to issue this stark reminder of the need to adhere to the Market Abuse Regulations. The furore and excitement of share dynamics can soon dispel as the reality of falling foul of the law hits hard.

The Financial Conduct Authority has issued its own statement following the SEC warning:

Other shares targeted by Reddit traders are surging at the US open:

Johnson & Johnson shares are down 3% in pre-market trading at $164.

That’s amid fresh reports about the efficacy of its own vaccine, which is lower than those for two others including the Pfizer/BioNTech and Moderna, which were around 95% effective.

As our global health editor Sarah Boseley reports:

A fifth vaccine, made by the US company Johnson & Johnson, has shown efficacy against the coronavirus and could transform prospects for protecting both the UK and the rest of the world, because it needs only a single dose.

The vaccine, made by the US giant’s subsidiary Janssen, based in the Netherlands, was trialled in the UK – and the British government has bought 30m doses. The EU has ordered 400m doses.

The company said it had 72% efficacy in preventing Covid in the US but a lower rate of 66% was observed globally in the large trial conducted across three continents and against multiple variants.

The results of the trials have been much anticipated, because the Janssen vaccine can be given as a single injection. That means stocks will go further, and particularly in lower-income countries an immunisation programme will be easier as there is no need for a recall after three or 12 weeks.

US futures are pointing to a negative start on Wall Street, reversing gains made at the end of Thursday’s trading session:

• Dow futures are down 0.97%
• S&P 500 futures are down 0.85%
• Nasdaq futures are down 0.79%

Robinhood, the app favoured by small investors who have sent the share price of certain stocks soaring, has secured a $1bn (£730m) injection from backers to handle the ongoing market frenzy, our media business correspondent Mark Sweney reports.

Robinhood has tapped existing investors and drawn down at least several hundred million dollars via a credit facility from banks led by JPMorgan including Morgan Stanley, Goldman Sachs and Barclays.

A spokesperson for Robinhood early on Friday described the $1bn injection as a “strong sign of confidence” that will help it “further serve our customers”.

Robinhood also contacted existing investors, which include Sequoia Capital and Ribbit Capital, about emergency funding, according to the New York Times.

It comes after the restore trading in companies including GameStop, after temporarily restricting access for the most targeted stocks.

The move to stop trades outraged users of Robinhood, which says its mission is to “democratise finance for all”, and sparked questions from US politicians.

Our full story will be posted shortly.

Need to catch up on the Wall Street trading frenzy? The folks over at Planet Money have come up with an amusing explanation on their TikTok channel.

Enjoy.

Concerns are mounting over whether financial markets have entered into bubble territory, given the stellar rise of some stocks and the never-ending news about new record highs for US indices.

It raises another key question: if we are in a bubble, is it about to burst?

Frédérique Carrier, head of investment strategy at RBC Wealth Management, says there are some interesting comparisons to be drawn with the dotcom bubble of the late 1990s, including cheap credit or easy money, that could disappear when the pandemic ends and credit conditions tighten.

However, she seems less convinced that we’re about to see the same chaos, partly due to the fact that stock market valuations do not seem as elevated as they did ahead of the dotcom collapse:

On the surface, U.S. equities appear expensive at 22.3x the 2021 consensus earnings estimate for the S&P 500.

After excluding the five largest technology-driven stocks (Apple, Amazon, Microsoft, Google, and Facebook), which constitute more than 20 percent of the S&P 500’s market capitalisation, the forward price-to-earnings (P/E) ratio drops to 17.5x, according to our national research correspondent.

This compares to a 10-year average of 16.4x for the S&P 500 as a whole, suggesting to us that while valuations are expensive, they are not significantly overvalued.

She says the Fed is likely to keep monetary policy loose, even if inflation picks up, given that a full economic recover from Covid is still a few years away. Stimulus also also likely to keep flowing.

But Carrier says this doesn’t mean investors shouldn’t be cautious:

Still, a pullback or correction cannot be ruled out, as much enthusiasm seems discounted in equity prices.

The frothiest, most extended parts of the U.S. market would be most vulnerable, in our opinion.

Difficulties with vaccine rollouts and delays in reopening economies that lead to disappointing earnings guidance could all trigger profit-taking.

European indices are still solidly in the red:

• FTSE 100 is down 1%
• FTSE 250 is down 0.7%
• Germany’s DAX is down 0.9%
• France’s CAC 40 is down 1%
• Italy’s FTSE MIB is down 1.2%

The FTSE 100 has now lost all of the gains it made at the start of the month.

Unless there’s an uptick before the end of the session, London’s blue chip index will have dropped around 1.5% in the first 30 days of 2021.

About 22 senior staff at Dr Martens have become paper multimillionaires overnight, receiving share awards worth more than £350m in the flotation.

They include the chief executive, Kenny Wilson, who joined the company in 2018 and is in line for a stake worth more than £60m. He previously worked for Cath Kidston, which collapsed last year.

Dr Martens’ chairman, Paul Mason, who was once the chief executive of Asda, will also receive a multimillion-pound windfall.

It came after the British boot company confirmed it would make it its stock market debut at 370p a share, giving it a valuation of £3.7bn at the top end of its range after keen investor demand for the famous boot brand meant the offer was eight times oversubscribed.

Shares were up 16% to 425p in conditional trading on Friday, among investors who were allocated shares in the IPO, but full market trading begins on 3 February.

Other stocks targeted by Reddit traders including cinema chain AMC and handset company Blackberry are rising in after hours trading:

• AMC is up 63% at $13.99
• BlackBerry is up 19% at around $17.19
• Bed, Bath & Beyond is up 16% at $39.30

Next up? Analysts say message boards points towards a potential jump in metal prices.

Neil Wilson, chief market analyst for Markets.com, says:

Keep an eye on silver – the /wallstreetbets thread is laced with mentions of effecting a massive short squeeze on the metal.

Yesterday we did see a sharp spike higher but it coincided with a swift reversal for the US dollar and gold also shot higher.

One to watch though.

Elon Musk has whipped up fresh interest in Bitcoin after changing his Twitter bio to say, well, just Bitcoin.

The cryptocurrency is now trading higher by around 11% at roughly $36,872.

The Tesla boss has been revered by many small retail traders taking part in the trading frenzy.

DATA UPDATE: German unemployment and Q4 GDP figures are out.

Economic performance was broadly in line with expectations, with German GDP rising just 0.1% in the final three months 2020 compared to the previous quarter.

But unemployment figures for January delivered a surprise. While analysts had expected the number of people unemployed in Europe’s largest economy to rise by 6,000, jobless numbers actually fell by 41,000.

Germany’s unemployment rate currently sits at 6%.

Speaking of which, US-based Novavax has seen shares jump 26% in after hours trading to $167.50 each.

Conor Campbell, a financial analyst at SpreadEx, notes that the retail trading frenzy is overshadowing positive news of the Novavax vaccine, which has been shown to be 90% effective in a UK trial.

He says:

The Reddit revolution has done a number on the European and US markets, scaring investors away from the message board-led volatility.

Of course, it’s not the Gamestop-saga alone. The vaccine rollout process in Europe has hit a confidence-undermining road bump this week, with the public spat between the UK, EU and AstraZeneca, while an end to lockdown in the UK appears nowhere in sight.

It is telling how risk-off investors are feeling this Friday that news the Novavax Covid-19 vaccine is nearly 90% effective – including against the UK variant – failed to induce the same dose of optimism as previous announcements of its kind.

Instead the markets opened Friday awash with red. The FTSE fell another 0.9%, this time despite the pound’s own reversal against the dollar and the euro.

Completing the erasure of the blockbuster growth that opened 2021, the UK index is now trading under 6,470, its worst price for over 5 weeks.

Facebook has taken down the popular Wall Street discussion group, Robinhood Stock Traders, in a move that its founder described as backlash for conversations buoying shares of GameStop Corp and other companies this week, Reuters reports.

Allen Tran, a 23-year-old from Chicago who created Robinhood Stock Traders, said he woke up on Wednesday to a notification that Facebook had disabled the 157,000-member group.

The notification, seen by Reuters, said without detail that the group violated policies on “adult sexual exploitation”.

Tran, who also runs the 20,000-member HaiKhuu Trading group on chat app Discord, said he has never seen adult content on the Facebook group.

Facebook spokeswoman Kristen Morea said, “This group was removed for violating our Community Standards, unrelated to the ongoing stock frenzy.” She did not respond to requests to elaborate.

Tran said institutional investors are trying to separate retail traders.

In other news this morning, fast fashion retailer Boohoo confirmed it has entered into exclusive talks to buy the Dorothy Perkins, Wallis and Burton brands from Sir Philip Green’s fashion empire, Arcadia Group, which collapsed into administration last year.

It has reportedly offered £25m for the trio of brands, but in an official statement, the company said:

These discussions may or may not result in agreement of a transaction. A further announcement will be made when appropriate.

The development comes days after Boohoo paid £55m to buy the 243-year old Debenhams brand in a deal that will result in the chain’s remaining 118 high street stores disappearing and the likely loss of 12,000 jobs.

Boohoo is expected to take the same approach and shut all Dorothy Perkins, Wallis and Burton high street store, keeping few existing staff.

Administrators have been seeking buyers for parts of Arcadia Group, which as a whole employed 13,000 staff and had 500 stores across the UK, since November.

Evans, its plus-size clothing brand, was sold to City Chic Collective, an Australian retailer, for £23m.

On Monday, the online fashion retailer Asos entered exclusive talks to buy the Arcadia brands Topshop, Topman, Miss Selfridge and HIIT. Topshop, Arcadia’s prime asset, could fetch between £250m and £300m.