Fifty-seven per cent of investors took out an Isa in the last tax year, the highest number since the tax wrapper's introduction in 1999, compared with 52 per cent in 2002, according to the IMA.
The most common Isa investment remains the mini Isa.
Although the cash component is still favoured by respondents, the stocks and shares option recorded 36 per cent compared with 28 per cent in 2002. The IMA says this could be seen as a good indication that investors' confidence in the economy is rising.
The number of investors saying they invested via a life insurance component rose from 3 per cent to 11 per cent.
Basic-rate taxpayers represented the majority of Isa investors, with 55 per cent of the total.
IMA communications officer Helen Stephenson says: “The increasing popularity of Isas among basic-rate taxpayers this year is proof of what a well designed, simple accessible product can achieve.
“The IMA will continue to lobby the Government for the creation of a single regulatory framework for pensions, Isas and the child trust fund in order to streamline a somewhat disjointed long-term savings policy.”