The system is still not "perfect", following the introduction of new voluntary guidelines on ISA transfers.
The four-week deadline for cash ISA transfers might not always be met by financial firms, the BBC reports.
Last month, the British Bankers' Association (BBA), the Building Societies Association and the Tax Incentivised Savings Association unveiled reforms of the process, involving a promise for ISA providers to communicate more with each other in order to speed the process up to 23 working days.
The tight ISA transfer deadline was introduced by the organisations, following customer complaints that they were missing out on interest payments due to delays in switching accounts. This situation is particularly acute at the turn of the financial year in April, when many financial firms introduce attractive headline rates on their accounts in a bid to attract new investments.
However, these guidelines are voluntary rather than mandatory - meaning that providers are not legally obliged to get the transfers done by this time.
Speaking to the broadcaster, BBA chief executive Angela Knight said that the reforms were ongoing, and would continue in order to shorten the transfer times with improvements to technology. "We want to move to electronic transfer [rather than the current system of paperwork and cheques] now we know that we've got a product that is going to stay and is not going to change," she said.
Ms Knight added that while it was "not the intention" of the BBA for customers to suffer "dead areas" as far as interest is concerned, she could not promise that "everything will be perfect with every ISA manager every time".
