More than a third of households have a tax-free ISA, with the popularity of the accounts soaring by 53 per cent since their launch, research showed today.
There were 14.2 million ISAs, in cash and stocks and shares, at the end of March last year, up from 9.3 million in March 2000 - a year after they were set up, according to Halifax.
The group said at least one person in 37 per cent of households had an ISA, with people in the South-East most likely to have one, at 44 per cent.
Savers paid £37.48 billion into the accounts during the 2008/09 tax year, 32 per cent more than was invested in 2000.
But the average amount paid into each account has fallen, dropping to £2,636 last year, down from £3,064 in 1999/2000.
People collectively had £169.5 billion held in ISAs at the end of last year, an 11-fold increase in real terms on the £12.3 billion ISAs held in March 2000.
Cash ISAs were more popular than their stocks and shares equivalent, accounting for 58 per cent of all money saved last year, despite the fact that people have the option of saving twice as much into shares accounts.
The situation is very different to when the product was launched in 1999, when 90 per cent of money invested during the first year was put into stocks and shares accounts.
Suren Thiru, economist at Halifax, said: "It's clear that ISAs hold an enduring appeal with savers with take up growing some 53 per cent over its history."
The over 50s can save up to £10,200 each tax year into an ISA, up to £5,100 of which can be in a cash account.
Those under 50 can save up to £7,200 each year, including up to £3,600 in cash, but their limits will rise to be in line with those for the over 50s from the start of the new tax year in April.
