Analysts at Barclays have expressed "surprise" at high pricing at the lower end of the platform market.
In a note commenting on the fortunes of leading asset managers, the bank said platforms had taken advantage of the Retail Distribution Review (RDR) to convert pricing models to increase charges for clients with investments of about £50,000.
"We were surprised to see IFA platforms' new clean pricing to be somewhat more expensive than historical expectations of the 25bps," the note read.
"We believe that this could be explained by some platforms taking advantage of the change to convert pricing more favourably. There is particular evidence of upwards pricing trends for smaller investors, from which the platforms previously made little money."
A number of platforms have tiered charging structures that heavily favour large investments, with fees on a £50,000 ISA charged at up to 77bps.
But providers looking to offer low-cost options to advisers and direct clients may also suffer competing against platform giants like Hargreaves Lansdown, the report warned.
"The effect of brand trust on investor behaviours is not to be underestimated. [FSA research] supports this, concluding that the strength of a platform brand plays a key role in initial platform selection. Once on the platform, there is a little evidence of switching.
"We are sceptical on the success of low-cost platforms, which charge more on a transactional basis. These small platforms have low AUA, have little editorial, do not own their own technology, and generally have relatively unknown brands. Their small size and unlisted capital structure means perhaps they have less financial firepower to aggressively market to customers.
"By offering a ‘no-frills' online service, we believe these smaller players are less likely to have customer service departments to help on-board new customers or support existing ones when they have a one-off transaction to make.
"A single bad experience can put off the customer from repeat transactions, especially when tying in psychological attachment to their lifetime savings."
The top four "main players" will continue to dominate the D2C market, Barclays added.
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