The letter said that over 80% of UK defined contribution pension assets are invested in listed securities, representing around 20% of the UK’s assets.

Mr Johnson and Mr Sunak asked that pension providers and savers invest more in long-term illiquid UK assets to boost economic recovery.

The letter has come under criticism from some pension providers and investment platforms who have accused Mr Johnson and Mr Sunak of attempting to push pension investors towards investments that may not be in their best interests.

Tom Selby, head of retirement policy at investment platform AJ Bell, said that just because the Prime Minister and Chancellor click their fingers does not mean pension investors will listen.

He said: “The reality is that pension scheme trustees have a duty to invest members’ hard-earned retirement pots sensibly, considering various factors including risk appetite, cost and, increasingly, impact on the environment.”

“Ultimately, the main job of pension schemes is to invest in a way that maximises returns for their members, not in the way the Prime Minister tells them to.

“While the focus here is on institutional money, retail investors should also think very carefully before piling into illiquid UK assets.

“Such assets may offer growth opportunities but can come with extra risks. This was most famously demonstrated in the collapse of Woodford Investment Management, which backed illiquid start-up companies and ended up unable to sell them quick enough to get cash to investors.

“Of course illiquid investments can be perfectly appropriate, but should only be considered if they fit with your retirement goals and risk appetite.”