However, Tom Selby, of investment service AJ Bell, said it was savers’ money at risk if investments backfired.
He said: “My overarching concern is that the needs of the saver, whose money is ultimately going to be risked, is going to be forgotten about.
“There’s a reason that an occupational scheme has a trustee to look after the interests of members. Part of it is investing their money to maximise returns and get the best retirement outcomes possible.
“Conflating a government goal of driving investment in the UK and people’s retirement outcomes brings a danger because the risks are all taken with members’ money.
“If it goes well, everyone can celebrate. But it’s clearly possible that it will go the other way, so there needs to be some caution in this push to use other people’s money to drive economic growth.”
The Government hopes its “radical action” will deliver around £80bn of investment overall, and boost defined contribution savers’ pension pots.
However, other experts were quick to cast doubt on whether Ms Reeves’s plans would work in practice.
Tom McPhail, of pensions consultancy the Lang Cat, said: “Merging together local schemes makes sense, as it benefits from economies of scale – nobody would deny that.
“But the Chancellor is simply assuming that this consolidation will lead to pension schemes investing more money in the UK economy.
“She says that carbon capture and restructuring the electricity grid are good things. But if I wanted investment advice, I wouldn’t go to Rachel Reeves.
“Pension scheme trustees have to put their fiduciary duty to their members ahead of the Government’s political agenda.”
Jon Greer, of wealth manager Quilter, said: “Large funds need substantial, reliable projects to generate returns, but the market may struggle to offer enough of these opportunities, especially in the infrastructure sector.
“If too much money chases too few viable investments, the effectiveness of this consolidation could be diluted, with funds potentially forced into riskier or less impactful projects.
“The Government will need to work actively to develop a pipeline of investable opportunities that align with the megafunds’ scale and risk requirements.”