How do you marinate a polar bear? Greenpeace protesters hi-jack Delia Smith online Q&A

There aren’t many culinary queries that can stump Delia Smith. “How do I marinate a polar bear?” appears to be one of them.

Waitrose, which has a lucrative advertising deal with Britain’s top chef, has become embroiled in an ill-tempered row with Greenpeace over a controversial partnership with the oil firm Shell – and environmental campaigners chose an online Q&A session with Ms Smith to make their feelings known.

Angry campaigners hi-jacked Waitrose’s Facebook page, challenging the chef over Shell’s plans to drill for oil in the Arctic – home to threatened species such as the polar bear and narwhal.

One comment read: “Hey Delia, I was looking for a way to marinade [sic] a polar bear but see Waitrose’s new partner Shell has the answer.” Another asked the celebrity chef for tips on cooking baked Alaska. Ms Smith studiously ignored the questions about Shell. Dozens of messages referring to the subject were deleted by Waitrose’s Facebook  administrator – which Greenpeace branded a “PR meltdown”.

The campaign, “Drop Shell” has the potential to severely damage Waitrose’s corporate reputation as one of the supermarket industry’s most ethical operators. It has trumpeted its commitment to environmentally sound farming and worked with Greenpeace to help source fish more sustainably.

Nearly 30,000 people have now signed a petition asking the supermarket to drop its deal with Shell, under which the oil firm manages 13 petrol stations outside Waitrose supermarkets. Waitrose customers can also receive Shell reward vouchers, and Waitrose products are available in two Shell forecourts.

“Waitrose built their brand on their ethical and environmental credibility,” said Greenpeace’s Sara Ayech, who has led the campaign. “A lot of customers shop there because they believe they are making an ethical choice. We want a positive statement from Waitrose saying that the Arctic is important to them and that they recognise the need to protect it.”

Shell attempted to drill in the Arctic for the first time earlier this year, after being granted permission by the US government. Despite investing $4.5bn in the project, the company was forced to delay drilling until next summer because of faulty equipment.

Waitrose said that their arrangement with Shell was “small”.