Alliance Trust Savings (ATS) is increasing the annual administration fee for the platform by up to £35 from the start of February.
From 1 February, the administration fee will rise from £40 to £75, before VAT, for an ISA/Investment Dealing Account and from £135 to £155 for its self-invested personal pension, Select SIPP.
Charges will remain at the new levels until 2016 at the earliest.
ATS managing director Patrick Mill (pictured) said: "We remain committed to a transparent flat fee model as the value of an individual account does not change the cost of administering it. We believe percentage charging structures are simply a tax on wealth.
"However, we have listened to feedback from our customers about the service we provide, our online service and the ad hoc charges that we apply to their accounts. Based on this feedback and the increased demand on our business, we have decided to move to a single, all-in-one administration fee which covers all regular activities customers carry out on their accounts."
ATS will offer free transfers until 28 February to customers who decide to move their investments. A loyalty discount is being introduced, starting for customers who have held an account with ATS for more than five years.
Customers who have held an account for between five and ten years will warrent a 10% discount on the standard £12.50 trading charge, rising to a 15% discount for accounts aged between 11 and 15 years, and 20% for accounts between 16 and 20 years.
Customers who have held an account for more than 20 years will qualify for a 25% discount on the online trading charge.
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