Separately, the amount of money that can be saved tax-free each year in a cash Isa is likely to be cut in the Budget.
The annual allowance is expected to be reduced from £20,000 to £12,000, as the Treasury wants to encourage people to invest instead.
That could help boost growth, a key objective for the government. But there are questions over whether people would naturally put their money into stocks and shares Isas as a result of the less generous tax break on cash Isas.
About a quarter of those who save money into a cash Isa currently save more than £12,000 a year.
Robin Fieth, chief executive of the Building Societies Association, which has campaigned against a cut, said: “A cut to £12,000 will not encourage more people to invest but will add unnecessary complexity, particularly around Isa transfers, and risks damaging the overall Isa brand.
“This may also deter people from saving and investing. The best way to build a culture of investing is on a strong culture of savings.”
