Regulators have been urged to intervene after an investigation revealed Amazon sellers are using hacked accounts to post five star reviews for themselves.

An investigation by Which? found legitimate Amazon users were having their accounts hijacked with one having as many as 2,500 bogus reviews posted in their name.

The consumer watchdog said after reporting the incidents some users had been told by Amazon they needed to delete the fake reviews themselves.

The investigation also uncovered sellers offering Amazon users cash and gift cards as bribes to rewrite negative reviews or post spurious glowing ones.

The findings have prompted Which? to call on the Competition and Markets Authority (CMA) to take action over the fake reviews on the online retail giant’s site.

Natalie Hitchins, Which? head of home products and services, said: "It is unacceptable that consumers continue to be misled into buying poor quality or even unsafe products by the current system of reviews and rankings.

"Online platforms must do more to tackle fake reviews, going above and beyond the current approach.

"If they fail to put more rigorous systems in place, then the CMA must intervene to ensure that fake reviews and other misleading tactics can be stamped out."