The free publication was produced in response to growing customer demand, the company said.

Client phone calls grew steadily through October with volumes ending the year at levels four times higher than those at the beginning of the quarter, it reported.

The guide explains who is likely to be impacted by the changes, how to calculate the value of an individual’s pension and the steps that those affected can take to minimise their tax bills, Fidelity said.

Richard Parkin, head of retirement at Fidelity International, said: “As April 2016 comes closer, the thorny issue of tax has, indeed, been taxing our customers.

“Without doubt, £1m is a lot of money for one person to acquire in pension saving but for those people who have been in a pension scheme for a long time – particularly those with final salary pensions – breaching the Lifetime Allowance could be surprisingly easy.

“Customers need to not only look at what they’ve got now but also think about the investment growth on all their retirement savings.

“A well-invested DC scheme coupled with one or two final salary schemes could put people close to the limit. We would urge anyone who is unsure to speak to an expert to assess their situation, as there are things they can do – for example apply for protection of their current savings or look at their withdrawal strategy.

“While there is no immediate rush to apply for protection, certain protections may require pension contributions to be ceased in March so it’s advisable to not leave this too long.”