A fringe Christian pressure group has attributed Tesco's recent poor sales to divine intervention, claiming that "God has answered our prayers for confusion in the Tesco boardroom".

Christian Voice, a prayer and campaigning organisation that claims to have nearly 2,000 members across the UK, protested outside Tesco shops towards the end of last year over the company's decision to sponsor a family area at the Gay Pride celebrations in London.

Tesco's stock market value plunged by almost £5bn this week after disappointing Christmas sales. The company's £500m Big Price Drop promotion apparently failed to tempt consumers away from rivals, and it has now warned of a drop in profit growth.

Christian Voice welcomed the developments, and claimed part of the responsibility for them.

"As the Big Price Drop was launched in September, it seems that almighty God, who operates outside space and time, was well ahead of us, anticipating our prayers, and seeing by our actions that our prayers were serious," Stephen Green, Christian Voice's National Director, said.

"Significantly, we prayed for a drop in their share price, which … has been answered on what you could describe as a biblical scale.

"I now call on Tesco to see sense before their company is ruined. Don't display the arrogance of Pharaoh. Withdraw the grant to Gay Pride."

A number of Christian commentators were angered by Tesco's involvement in Pride London. Francis Phillips, writing in the Catholic Herald, urged the company to "stop dabbling in dubious fringe political movements" and Colin Hart, the director of the Christian Institute, said he would not be shopping at the store over Christmas and urged others to do the same.

Green, whose organisation led the charge against the BBC for broadcasting the "blasphemous" Jerry Springer – the Opera in 2005, told the Guardian: "It's quite a good thing if Tesco are humbled – they're a bit too big for their boots."

Tesco declined to comment.