Banks and building societies are giving poor advice about cash Isa transfers.
In an undercover investigation, consumer group Which? found just three out of 104 calls to providers resulted in accurate answers to all four simple questions.
The probe involved mystery shoppers calling the top thirteen Isa providers (as held by Which? members) eight times each to test how well bank and building society staff explain cash Isa transfer rules.
The worst offender was found to be HSBC as it answered an average of 32% of questions correctly, followed by the Royal Bank of Scotland (35%), The Co-operative Bank and First Direct (both 38%).
Overall, most advisers (97%) gave conflicting and incorrect information about how much consumers could transfer and 43% were unaware you can move money from a cash Isa to a stocks and shares Isa.
One HSBC adviser even suggested the more money people had, the longer a transfer would take, which is inaccurate.
Nationwide scored best, answering 69% of questions correctly, followed by Barclays and Yorkshire Building Society (both 63%).
Which? chief executive, Peter Vicary-Smith says: "We were genuinely shocked by this Isa investigation.
"Cash Isa transfer rules aren't that complicated and cash Isas have been around since 1999 surely 12 years is long enough to learn the rules?"
Which? is urging the industry to better train its frontline staff, as well as calling for the introduction of electronic transfers for cash Isas to speed up the transfer process.
New transfer rules
New guidelines from the Office of Fair Trading, that came into force this year, state for cash Isas transfers can take no longer than 15 working days, down from the previous 23-day limit.
The overhaul followed a super-complaint launched by lobby group Consumer Focus in March last year, which stemmed from MoneySavingExpert.com's Moneyfesto.
Sarah Brooks, from Consumer Focus, says: "Our super-complaint showed consumers were getting a raw deal.
"Banks seem to be making a simple product unnecessarily complicated because of poor service, inaccurate or unclear information and inefficient systems which delay switching.
"At a time when the size of bonuses and profits are in the news, it is inexcusable that banks should fall down over something as basic as not training their staff properly."
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