Kate Ogden, an economist at IFS and one of the authors of the report, told PA older pension pots were generally less value for money.

She said: "It is vital that people get the most out of the retirement saving they have done over their working lives.

"This won't happen automatically.

"Older personal pensions risk becoming poor value for money.

"The fees charged are often higher than those on pensions taken out more recently.

"In addition, how they are invested can become less appropriate as individual circumstances change.

"Many would benefit from taking active decisions over their past pensions, and this needs to be made easier to do.

"But greater individual engagement will never completely fix this issue, and policymakers need to consider wider initiatives to encourage value for money in older pensions." 

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According to the IFS, research investment performance over a five-year period was similar regardless of whether they had higher and lower charges.

Older savers closer to retirement may have pensions invested in riskier investments, according to the research.

A spokesperson for the Association of British Insurers (ABI) said: "Today's pension market is competitive and it is much more straightforward to start saving or to consolidate pensions.

"We agree that more can be done to make it easier to make active decisions.

"A change in the advice rules would enable providers and guidance services to support savers further."