Billions of pounds are at risk as investment in cash individual savings accounts (ISAs) continues to soar, according to analysis from Royal London.
Newly released figures from HM Revenue and Customs reinforce the concern that investors are holding excessive amounts in the low-interest accounts, rather than diversified stocks and shares ISAs.
The surge into cash accounts follows a large increase in the limits for cash ISA investing in July 2014, when a previous annual cap on investment increased from £5,760 to £15,000.
"Saving in cash clearly has a part to play for short-term emergencies and rainy day savings," Royal London personal finance specialist, Helen Morrissey, said. "But a combination of low interest rates and rising inflation means that money in a cash ISA is losing spending power, year after year."
"While cash ISAs have a role to play investors must also consider the benefits of the investment returns gained from stocks and shares ISAs."
The Royal London analysis reveals that many of the cash ISAs may even deliver negative real returns once inflation is taken into consideration, with £100bn thought to have been lost over the last decade by investing in the accounts.
Aggregate figures for 2014-15 and 2015-16 show that £120bn was invested into cash ISAs over the period, compared with just £43bn in stocks and shares accounts.
In addition, it was found that investors with annual incomes under £30,000 per year were more likely to hold their ISA savings in cash only products in 2014-15, while the opposite was true for those that make more than that.
Younger people are also more likely to hold money in cash accounts, with the temptation to invest long-term savings in cash ISAs set to increase further, after the annual cap on investment increased to £20,000 last month.
"The data shows that lower income households and younger savers are particularly at risk of losing out," Morrissey continued.
"The government needs to think carefully about its ISA policy and should consider reintroducing separate lower limits for cash ISAs to avoid a 'dash for cash' costing savers dearly."