One third of UK earnings are now invested in cash individual savings accounts, with an average balance of £7,782.
People in Wales and Northern Ireland have the largest amount in their ISAs, they save around 37% of the average UK salary, according to a report by Halifax.
More than half of the top 30 local authorities with savers who have the highest cash ISA balances are in Greater London and the South East.
To find the best cash ISA rates, check out our round-up.
Those aged over 75 are the savviest savers, with an average amount of £13,912, while those aged 16-24 have only £1,848 in their cash ISAs, although this could be because they have had less time to build up their savings.
Regionally the highest average ISA balance of £10,4761 is in the Derbyshire Dales, 35% above the national average, and the smallest is £4,675 in the London borough of Hackney.
Two years ago, when the survey was last completed, the area with the largest average balance was Epsom and Ewell with an amount of £9,021.
Nitesh Patel, economist at Halifax, says although it’s good news people are taking advantage of the tax-free benefit of Isas, "frustratingly, savers are still not making the most of their savings by using their full annual allowance".
Patel says it’s encouraging to see older people saving more, which shows it's not just the younger generation who are financially savvy.
The maximum amount allowed in a cash Isa is £5,100 for this tax year. In the 2011-12 tax year the allowance will increase to £5,340.