A new tax-free Isa allowance that comes into force next month will allow wealthy couples to put more than £70,000 beyond the reach of HMRC.

Under previously announced changes, the current Isa allowance of £15,240 per person for the tax year 2016/17 will rise to £20,000 from 6 April. It means a couple who have not so far used this year’s allowance can move a total £70,480 into tax-free savings in the next few weeks.

Until this week the Isa sector had started to look redundant for all but those with very large sums to invest. The previous chancellor, George Osborne, introduced a series of measures that rendered them unnecessary for most ordinary savers. People can now earn up to £1,000 interest on cash savings, and were in line to obtain up to £5,000 in share dividends without having to declare it to the Treasury.

But this week’s budget announcement on share dividends looks set to revitalise Isas.

With the rates payable on cash Isas so poor – typically below 1% – investors are increasingly looking to share-based funds, particularly equity income funds. These try to achieve an annual income of around 4% from a basket of dividend-paying shares. Most stock market investors usually take out an Isa through an investment platform, such as those provided by the likes of Hargreaves Lansdown or Fidelity.

Experts have suggested Philip Hammond’s move could be a bonanza for the investment companies as wealthy consumers start shifting their money into Isa-based funds. Popular investments are likely to be the leading equity income funds, with funds from Woodford, Invesco Perpetual, Fidelity, Schroders and JOHCM regularly at the top of the best sellers lists. Over the past 10 years, the average equity income fund has produced total dividends of just over £4,000 from an investment of £10,000.

Those preferring to invest directly in dividend-paying shares can place them into an Isa, using a “bed and Isa” arrangement whereby they sell their existing investment and buy it back within the Isa, although they may incur a CGT bill.

A “market-leading” government-backed savings bond paying 2.2% will be available for 12 months from April, the chancellor confirmed this week, although no actual day has been named.

The three-year bond, which will be offered by National Savings & Investments, was first announced by Hammond in his November 2016 autumn statement. The government has previously said it expected about 2 million people to snap up the bond, which is aimed at those willing and able to tie up their money for three years. It will be open to everyone aged 16 and over and have a minimum investment limit of £100 and a maximum of £3,000.

The Treasury said the bond would support savers affected by low interest rates, but Maike Currie at investment firm Fidelity International said: “Anyone saving into the new investment bond will struggle to achieve a real return, with Office for Budget Responsibility expectations for inflation to rise to 2.4% in 2017, and 2.3% in 2018, before falling back to 2.0% in 2019.”