Royal Mail’s share price slumped on Tuesday to its lowest point since privatisation after declining junk mail and business uncertainty meant it delivered fewer letters.

Addressed letter volumes, excluding the impact of elections, fell by 8% year on year in the nine months to 23 December, while letter revenues fell by 6%.

Companies have been forced to scale back their mass mail marketing campaigns because of tighter EU privacy rules introduced under the General Data Protection Regulation. Meanwhile, businesses continue to shift from letters to email for communications with customers.

Rico Back, the Royal Mail chief executive, also blamed business uncertainty for letter declines, at a time when fears of a no-deal Brexit are seen as the main reason for companies holding back spending.

Shares fell by 10% to 270p in morning trading on Tuesday, having earlier hit their lowest point since the formerly state-owned company was floated at 330p in October 2013.

The privatisation was heavily criticised after taxpayers missed out on an estimated £1bn to the benefit of City investors for the underpriced float. However, Royal Mail has faced a series of challenges in the past year that have seen shares fall from heights above 632p in May.

The share price fall means the value of company, which was demoted from the FTSE 100 in December, is below £3bn.

Royal Mail in November launched a big cost-cutting programme, including a plan to share more costs between its letters and parcels businesses. Initial cost cuts did not progress at the rate expected after a deal with unions failed to improve productivity.

On Tuesday Royal Mail said it was on track to trim £100m in 2018-19 in the UK. However, it warned that cost pressures in its European and US operations were continuing.

Royal Mail also faced a major shareholder revolt over Back’s pay in July. MPs described as “astounding” a £5.8m payout to secure the new chief executive, who succeeded Moya Greene in June.

Back said trading over the nine months to 23 December was “broadly in line with our expectations”. However, he said the company expected operating profit before restructuring costs of between £500m and £530m for the 2018-19 financial year – below the £500m-£550m guidance given in its last profit warning in October.

City investors on Tuesday said the company should contemplate radical options as part of any turnaround plan.

John Moore, senior investment manager at Brewin Dolphin, said: “At this point of uncertainty, some vision for the future from management – be that a further cost-saving programme or a strategic move on [European parcels business] GLS – would be a welcome focus for investors.”

Royal Mail expects letter volumes to fall by 7% to 8% in the 2018-19 financial year, but said its previous forecasts for next year were likely to be too optimistic.

Royal Mail’s overall revenues rose by 2% in the nine months to 23 December. Revenues were boosted by growth in parcel volumes, which have been buoyed by the increase in online shopping. Royal Mail handled 164m parcels in the December trading period, up by 10% over the previous year.