According to the findings, over two in five (42 per cent) UK adults currently direct money into an ISA (71 per cent cash and 23 per cent stocks & shares), with one in ten ISA holders having set up their ISA for the first time this tax year.

However, the relative popularity of ISAs masks weak knowledge of the returns achieved. The report reveals that just under seven million ISA holders (22 per cent) are in the dark as to what returns they might be achieving from their cash or investments, and just one in five (18 per cent) are confident they know exactly what they are getting.

The research also reveals that ISA savers and investors are not reviewing their savings and investments frequently enough. According to Nutmeg’s research, over a third (34 per cent) of ISA holders review their pots less than once every six months; a further 15 per cent say they never review, despite more than twice that number being well aware they could be missing out on better returns.

Of those who do who don’t review their ISAs, two in five (40 per cent) say they can’t be bothered to review their savings, and a third (33 per cent) say they are not interested in reviewing.

“The Financial Services industry must shoulder some responsibility for this sorry state of affairs,” said Nick Hungerford, CEO and founder of Nutmeg. “Companies have made personal finance so complicated; as a result customers aren’t motivated to shop around for the best deals and to maximise their opportunities.”

“Our research exposes the incredible amount of apathy that exists among consumers. We must demonstrate just how dangerous it is to disengage from savings plans. ISA holders shouldn’t just leave their cash or investments unattended. If customers don’t have the time to manage their investments regularly, they must find someone to do it for them. ”