The Christian Institute is backing a boycott of the supermarket Tesco after one of its employees wrote on his personal Flickr page three years ago that he would campaign against “evil” Christians who oppose marriage equality.

Tesco has been criticised by the organisation in recent months for reducing the sizeable financial support it has offered Cancer Research UK over the last ten years, while giving Pride London £30,000 to fund its family area.

The religious charity slammed Tesco for its Pride London donation, which amounts to only 0.05% of the retailer’s £63.4 million of annual charitable giving.

The £30,000 Tesco pledged is equivalent to 0.008% of the amount Cancer Research UK’s Race for Life events have raised since 1994.

The comments in question were made by Tesco’s Head of Research and Development, Nick Lansley, in 2008 on his personal Flickr account and were subsequently removed.

His comment read: “I’m also campaigning against evil Christians (that’s not all Christians, just bad ones) who think that gay people should not lead happy lives and get married to their same-sex partners.”

In its instructions on how to boycott the retailer, the Christian Institute drew attention to the case of Adrian Smith, who was demoted for commenting on his personal Facebook account that gay marriage was an “equality too far”.

Last week, Peter Tatchell said he would testify in defence of Adrian Smith, whose comments he said were made in a “calm, non-abusive manner. He was not threatening or intimidating.”

Although the Christian organisation heavily criticised the decision in Mr Smith’s case, it appears to call for similarly far-reaching repercussions for Mr Lansley’s retracted comment.

Director of The Christian Institute, Colin Hart, said: “I won’t be shopping at Tesco this Christmas, and I am repeatedly hearing from other Christians who have already come to the same conclusion.

“Mr Lansley is entitled to his opinions, and Christians are entitled to choose not to shop at Tesco.”

Tesco told PinkNews.co.uk it could not comment as the remark was made on Mr Lansley’s personal Flickr account. Mr Lansley was also unable to comment.

In 2006, footage of Mr Lansley’s civil partnership ceremony was made a “recommended video” on Youtube, and was viewed nearly a quarter of a million times.

Over a thousand comments were left on the video, including one saying: “Matrimony is a sacrament established by God between MAN and WOMAN not for faggots and lesbians”. Another added “Don’t provoke God to anger, fags”.

On Friday, the Christian Institute provided supporters with the email address of Tesco’s CEO and a link to their Facebook page, instructing readers: “If you won’t be shopping at Tesco this Christmas, tell them so”.

Formed in 1990 by a group of church leaders and Christian professionals, the Christian Institute has funded many cases where the religion and gay rights have clashed.

The Institute describes itself as a “non-denominational Christian charity committed to upholding the truths of the Bible.”

The Christian Institute also backs the ill-fated challenge to civil partnership regulations which, it was claimed, could force religious institutions to hold civil partnership ceremonies. The House of Lords rejected the argument last week.