Liberal Democrat president Tim Farron has apologised for the wording of a letter which called for a ban on adverts that claimed God could heal sick people to be overturned, but stood by his belief that prayer could help.
The MP for Westmorland and Lonsdale lent his name to a letter delivered to the Advertising Standards Agency which challenged the watchdog to provide "indisputable scientific evidence" that prayer could not heal the sick.
Farron, along with Tory MPs Gary Streeter and Labour MP Gavin Shuker, wrote to the ASA following its decision to ban an advert in Bath that included the line: "NEED HEALING? GOD CAN HEAL TODAY!"
The ASA ruled last month that the adverts could encourage "false hope" among people suffering from medical conditions.
In the letter, seen by Total Politics, the MPs said the ruling "appears to cut across two thousand years of Christian tradition and the very clear teaching in the Bible".
"Many of us have seen and experienced physical healing ourselves in our own families and churches and wonder why you have decided that this is not possible," they wrote.
In the letter, Streeter, claimed to have been healed by prayer himself.
"You might be interested to know that I received divine healing myself at a church meeting in 1983 on my right hand, which was in pain for many years," he wrote.
"After prayer at that meeting, my hand was immediately free from pain and has been ever since. What does the ASA say about that? I would be the first to accept that prayed for people do not always get healed, but sometimes they do. That is all this sincere group of Christians in Bath are claiming."
The three MPs also raised the case of footballer Fabrice Muamba who collapsed during a match on March 17.
"It is interesting to note that since the traumatic collapse of the footballer Fabrice Muamba the whole nation appears to be praying for a physical healing for him," the MPs said. "Are they wrong also and will you seek to intervene?"
"We invite your detailed response to this letter and unless you can persuade us that you have reached your ruling on the basis of indisputable scientific evidence, we intend to raise this matter in Parliament."
Following the publication of the letter Farron apologised to Liberal Democrat members, many of whom disagreed with his decision to sign the letter.
In a post on the grass-roots Liberal Democrat Voice website on Wednesday evening, Farron said it was "not a well-worded" and that he should not have signed it "as it was written".
"The reference to the ASA providing indisputable evidence is silly, and the implication that people should seek faith healing at the expense of medical intervention is something that I just don’t believe in," he said.
He added: "For what it’s worth, I also think that the Fabrice Muamba reference is crass. So on all those fronts, I should just say sorry and not bother defending myself. I shouldn’t have signed that letter as it was written, so I apologise for putting some of you in quite a difficult position."
However Farron stood by his belief that "prayer helps" and said the ASA "aren’t appointed to be the arbiter of theological matters" and had overstepped their remit.
"As a Christian I believe that prayer helps – although my belief is that God mostly heals through medicine, surgery and human compassion and ingenuity," he said.
Farron is on the social-democrat wing of the Lib Dems and is widely believed to be in with a good chance of succeeding Nick Clegg as the party's leader.
He also said he thought the ASA decision to ban the Bath advert offended his "Liberalism far more than it bothers me from a Christian perspective" as it was a restriction on free speech.
Since posting his response on Tuesday, Farron has engaged with both positive and negative comments on Twitter.