It is the wine he drinks and offers to his guests on his popular BBC chat show.

But today The Mail on Sunday can reveal Graham Norton has invested in the sauvignon blanc he swills on air - leading to claims that he has broken strict BBC advertising rules.

Last week it was revealed that the Irish star earned between £850,000 ($1.48 million) and £899,000 from the BBC, but he is actually the corporation's biggest earner. The 2016 accounts for his So Television company state he was paid £2.6m for "presenter fees, production fees and royalties", meaning he gets about £3.5m a year from the BBC.

Norton's backing for New Zealand firm Invivo Wines and their £9 bottles of "Graham Norton's Own Sauvignon Blanc" has seen annual sales rocket from 14,000 bottles in 2014 to two million this year.

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Strict BBC guidelines say presenters should not appear on air using products in which they have any financial interest, and marketing material should not refer to their BBC programmes.

But Invivo Wines claimed on its website that it was "the wine of choice for UK chat-show star Graham Norton and his guests".

The boast was removed yesterday after inquiries from this newspaper.

But in another apparent breach of the rules, a promotional online video for Invivo Wines was filmed on the set of Norton's show. The footage, shot during pre-show rehearsals, showed Norton - who has a 2 per cent share in the wine firm - crushing grapes.

Damian Collins, chairman of the Commons Media Select Committee, said: "I want to know why the BBC thinks this is OK. I don't think this is within the spirit of the guidelines. Using the branding and the set of the show to promote the product away from the show is drawing on the asset of the show, which is BBC property."

Last night, the BBC and a spokesman for Norton said the Invivo Wines marketing video was filmed in aid of charity in 2014.

However, there is no mention of a charity in the video.

A BBC spokesman added: "No brands are promoted on The Graham Norton Show."