Aviva has apologised for "cross-selling" discounted private medical insurance (PMI) to advisers' clients, in what the insurer has said was a mistake.
Some clients who had bought PMI from Aviva via an IFA received a statement from the insurer offering a 5% discount on their premiums "for being a loyal customer".
After following a web-link to the offer page, however, customers are told the discount is for direct customers only, and "it is not available online or through an intermediary".
The clients' financial advisers also received copies of the statements.
Ian Green, an IFA at Green Financial who received the letter, said Aviva's behaviour was "very disappointing".
"It is taking an IFA-developed customer with a regulated product, and cross-selling their own direct, non-regulated product to them," he said.
"Over the last few years, Aviva have actually been very IFA-friendly, which is why this surprises me."
A spokesperson for Aviva apologised to advisers and said the letter was sent out by mistake.
"It was intended for direct customers only and unfortunately was issued in error," the spokesperson said.
Aviva plans to launch an investigation into how the mistake occurred, she said. A new letter is also being developed for intermediary customers.
In the past few months, providers have been accused of poaching clients from advisers by launching direct to consumer services (D2C).
In September, Friends Life was forced to defend their new service, PlanWise, from claims that it targeted IFAs' existing client bases.