The new rules – announced by Chancellor George Osborne in the 2014 Budget – allow British savers to squirrel away up to £15,000 a year tax-free, a significant boost from the previous allowance of £11,520.

However, knowledge of the changes is low, with 23 per cent of people saying they are not aware of the new rules.

Awareness was lowest among young people. Halifax found that 40 per cent of 18-24 year olds were unaware of the new rules, as were 36 per cent of 25-36 year olds.

However, people recognised the potential benefits of the higher limits – 61 per cent of people surveyed were able to identify some of the financial benefits, but 28 per cent said they would like more help in understanding the changes.

Some 32 per cent of cash ISA holders expect to save more now the allowance has increased, but more than half believe the increased limits will make no difference to their saving habits.

Richard Fearon, head of Halifax Savings, said: “The new ISA rules have the potential to transform the level of the UK’s savings. However, in the short-term there remains confusion about how much people can save in their ISA and when.

“As a result, many savers could already be missing out on the tax-free savings by being unaware that it’s possible to start saving now and top up to the full limit.”

Under the new rules, savers will have the option of putting the maximum £15,000 into whatever combination of cash or stocks & shares New ISA (NISA) they like and they will be able to transfer funds freely between cash and stocks and shares.