Close to half of the D2C platforms researched by the platform consultancy charged some form of exit fee for ISA transfers, while 87 per cent did so for self-invested personal pensions (SIPPs). More than half also charged for stock transfers.

By contrast, just 13 per cent of adviser platforms levied exit fees for ISA transfers and stock transfers, and only a third charged for SIPPs.

Lang cat research manager Steven Nelson said: “There is a lot of industry focus on things like super clean share classes and discounted fees. But, on average, that makes up a fraction of any portfolio, whereas the exit fees can be large.”

Such fees undermine the freedom of choice platforms are supposed to offer, he suggested: “Exit fees should not be punitive. You can maybe see the argument for a few pounds to justify the administrative costs, but platforms are meant to be technological solutions.”

The lang cat research is based on quoted fees from platforms, and does not discount the fact other platforms may be charging undisclosed fees.

Alliance Trust requires £100 to transfer an ISA, while D2C platforms Barclays Stockbrokers, James Hay, and TD Direct all charge £50. Barclays charges the most per stock transfer, at £30.

Platform giant Hargreaves Lansdown is also among those charging exit fees, with its D2C platform charging a £25 exit fee on both SIPPs and ISAs, and a £25 fee per stock transfer. Up-and-coming rival Nutmeg charges between £0 and £40 exit fees for ISAs depending on the speed of withdrawal.

Chelsea Financial Services managing director Darius McDermott has called for exit fees to be banned.

He said: “We are in the D2C space but we do not charges exit fees. I just cannot see any justification for it being more prevalent in the D2C market than the adviser market.”

He questioned why platforms felt the need to erect barriers to prevent clients leaving.

 “There is going to be the odd client who has moved on but, over a long period of time, you should be able to lose the odd one or two. If the client wants to leave, why should they have to pay to get off a platform to pay for another platform?”

Charles Stanley Direct’s head of investment research Ben Yearsley said exit fees are a “legitimate charge” but added the fee must be fair.

“It is a necessary evil, but the likely question is ‘what is a fair charge?’ What you do not want is people slipping from one platform to the next to get the best short-term deal.”