Two of the UK’s largest power companies have quietly transferred the ownership of their British operations to offshore companies to protect themselves against Labour’s plan for renationalisation.

National Grid and SSE, which together own Britain’s gas and electricity transmission networks, confirmed on Sunday they had created overseas holding companies following Labour’s pledge to restore them to state ownership.

SSE has put its UK business into a new Swiss holding company while National Grid has shifted its gas and electricity businesses into subsidiaries in Luxembourg and Hong Kong.

The decisions, which follows a similar move by two water companies, are designed to protect their shareholders against any move to buy back the firms without paying what they would consider to be the full market value.

Last week, Jeremy Corbyn unveiled Labour’s most radical manifesto in decades, including the pledge to reverse several of the privatisations of the 1980s and 90s. The party aims to renationalise the rail, water and electricity industries, as well as BT’s broadband infrastructure division, Openreach, if it is wins the election.

SSE, which has a market value of almost £14bn, confirmed it had moved its electricity distribution business, which supplies 3.7m homes, plus its high-voltage electricity transmission network to a Swiss holding company.

It said: “SSE has incorporated in Switzerland a direct and wholly owned subsidiary company to acquire, oversee and hold investments or other financial assets.

“The company has become the holding company for SSE’s electricity transmission and distribution networks through a share-for-share exchange. This is intended to support long-term investment in low-carbon infrastructure in SSE’s core businesses.”

SSE said there were no profit or tax advantages of such a move and it was fully consistent with SSE’s commitment to fair taxation.

National Grid, which is worth more than £30bn, connects England and Wales’s regional power companies with large power stations via almost 6,000 miles of power cables. It also owns the main gas transmission pipelines.

“Labour’s proposals for state ownership of National Grid would be highly detrimental to millions of ordinary people who either hold shares in the company or through their pension funds – which include several local authority pension funds,” it said in a statement.

“To protect their holdings, and in line with our legal fiduciary duty to our shareholders, we have established holding companies in Luxembourg and Hong Kong. This has no financial benefit to the company and does not affect its day-to-day operations. It is solely to protect our shareholders’ interests.”

While the offshoring of ownership would not prevent renationalisation, the utilities hope it would force a Labour government to pay more to take back the assets. The fear is that a Labour cabinet would issue a compulsory purchase order on the companies’ shares at a price below market value and double the pain by offering shareholders low-returning government bonds as compensation.

Switzerland, Luxembourg and Hong Kong have bilateral investment treaties with the UK that ensure investors are paid the market rate in the event of any state asset buy-back. It is believed the move could also protect the firms’ directors from litigation by disgruntled shareholders.

Analysts have already said Labour’s plan would have a negative impact on private shareholders who own shares in the utility firms. Pension funds would also take a big hit if the move failed to restore the full market value of firms taken back into public ownership. Both SSE and National Grid have been prized in recent years for their dependable returns to shareholders.

The Energy Networks Association trade body has claimed the renationalisation plan would lead to delays to decarbonisation of the UK.

“It would lead to reduced public accountability, disruption to innovation and higher costs to bill payers. Time to reach net zero is running out – let’s not waste it by needlessly scrapping a system that works,” it said.

Anglian Water is among the utilities to have already created overseas holding companies, and it is understood that Severn Trent is contemplating a similar move.

The Labour party said: “The UK’s energy networks are vital strategic infrastructure on which we all rely. You cannot boil a kettle, heat your home or run a business without the grid. The idea that private owners, who have been ripping off the public, would move offshore in an attempt to prolong the rip-off illustrates just why we need the grid back in public hands.”

• This article was amended on 25 November 2019. An earlier version stated that Yorkshire Water was among the utilities to have created an overseas holding company. This was wrong and has been removed.