One of the best-known names in the furniture industry has hit out at retailer-turned-TV personality Mary Portas, accusing her new series Secret Shopper of being “morally indefensible”.

A letter sent by Furniture Village chief executive Peter Harrison to every member of Channel 4’s board - including its chairman, former Marks & Spencer chairman Lord Burns - alleges the programme is a “biased, ill-informed perversion of the truth” and accuses Portas of “entrapment” of store staff. The letter, seen by Retail Week, says sales fell as a result of the programme.

In the series, which concluded this week, Portas went undercover in stores with the aim of highlighting poor service, but the tactics have angered retailers. Others targeted in the programme included Primark, H&M, ScS and New Look.

Portas remained defiant this week, standing by the programme and her criticism of retailers.

“I do think that generally service in this country is appalling,” she told Retail Week. She claimed customers appreciated her crusade. “Some will dislike me, but a lot more love what I’m doing,” she said.

In one episode, Portas said Furniture Village’s stores looked like a prison and accused a member of its staff of encouraging consumers to commit fraud by explaining how to make a claim on an insurance plan.

The allegations were made in writing to the retailer six weeks after the undercover filming, but left it only one day in which to respond.