According to analysis by JP Morgan Asset Management going back 11 years, the ‘ISA season’ phenomenon, where activity is concentrated in the first few months of the year, could mean investors are at the risk of not fully making their funds work for them throughout the year.

The analysis suggests investors are increasingly investing around the turn of the tax year rather than in the months leading up to the 5 April deadline.

Keith Evins, head of UK Funds Marketing at J.P. Morgan Asset Management, said: “The sales data for investment ISAs in recent years almost suggests panic-buying – as if people know they need to use their allowance, but don’t make their buying decisions until the very last minute.

“Looking at the figures from 10 or so years ago, there is a much clearer and more gradual step-up in buying activity across the first quarter, although the amount that people were investing in stocks and shares ISAs was evidently hit by the market slumps in 2003 and 2008/9.”

The data, for net sales of open-ended funds within an ISA wrapper, shows that in each year since 2002, April has been the best-selling month for unit trust and OEIC ISAs.

However, where there used to be a gradual and smooth pick-up in activity from the start of the calendar year to the end of the tax year, the last three years have seen declining net sales in March yet increasing sales in April.

Evins added: “The big spike in April sales could reflect ‘early birds’ investing their new year’s ISA allowance as well as those who have left it to the last minute. Because of the ‘use it or lose it’ nature of the ISA allowance, there will always be an element of seasonality in buying behaviour.

“But with studies consistently showing the value of regular investment, and the impossibility of knowing whether markets will plummet or surge the day after your lump sum goes in, we would argue that even if you have a lump sum you might be better off investing it in stages.

“For the many people who do not have a lump sum, regular investing – even if it is £50 a month – is an affordable way of building a meaningful savings pot for the future.”