The organisation estimates that between 34 per cent and 44 per cent of pensioners will fail to realise their full pension credit entitlements and will miss out on as much as £2 billion by failing to apply.

And IFA Promotion also says that working people in company pension schemes are missing out on huge sums by neglecting to save in tax-efficient ways.

It claims high-rate taxpayers that are covered for their retirement by a company pension scheme will gift an unnecessary extra £656 million to the tax man this year by failing to make Additional Voluntary Contributions.

David Elms, chief executive of unbiased.co.uk, said: "Under-provision for retirement remains a crucial problem for the UK and those that are in a position to save more should be doing so.

"However, it seems that people are compounding the situation – be it through apathy or confusion – by failing to claim vital sources of retirement income in the form of tax credits.

"Likewise," he added, "retirement savers are not making things any easier for themselves by overlooking the need to top-up their company pension pot."

IFA Promotion advises anyone unsure of their tax credit entitlements to contact their local independent financial advisor.