An influential inquiry into the future of Britain's abortion laws will begin today amid controversy over an apparent attempt by faith-based organisations to skew the balance of evidence presented to the committee of MPs.

At least eight submissions of written evidence have come from medical professionals who have not disclosed their membership of Christian groups opposed to abortion on faith grounds. Six of the doctors are members or activists with the Christian Medical Fellowship, an organisation that has given its own evidence to the inquiry.

Suspicion that contributors had not been transparent about their affiliations has led the clerk of the committee to take the unusual step of writing to all those who gave evidence asking them to disclose their links to any relevant organisations.

The committee is examining recent scientific evidence on issues such as the long-term impact of abortion on the mother's health and whether babies born younger than 24 weeks (the current limit for most abortions) can survive. The inquiry's terms of reference specifically focus on scientific considerations and not ethical and moral arguments.

Some on the committee are worried that unless witnesses are transparent about their affiliation to anti-abortion groups the inquiry will not be able to properly assess their evidence.

Evan Harris MP, the Liberal Democrats' science spokesperson, said: "This inquiry is specifically about the scientific evidence not moral or religious arguments and our witnesses need to be evidence-led not ideologically or theologically driven. The CMF risk undermining the inquiry by getting people called as expert scientific witnesses when they are not."

Two witnesses who will give evidence today, Chris Richards, a paediatrician and honorary clinical lecturer at Newcastle University, and John Wyatt, a neonatal paediatrician at University College London, are members of CMF, but did not disclose that on their original submission.

"Everyone is entitled to an opinion but when non-experts are submitting their views about findings they really ought to declare where they are coming from so their expertise and standpoint is not misunderstood," Dr Harris said.

Professor Wyatt, who sits on CMF's public policy committee, said: "I'm basically giving this submission as a private individual not a representative of any organisation. It doesn't seem to me helpful in a way to wish to diminish the impact of evidence according to the personal beliefs of the people who present them, unless one is going to do that across the board ... what we are asking is for scientific evidence to be considered on its merits and avoid a sort of polarisation which so easily comes into this field."

He added: "The idea that people can give information without people finding out where they are coming from - that there is some attempt to hide - is surely ludicrous in the age of Google."

In an article in autumn 2005 on the CMF website he wrote that "CMF has played an important and increasing role in making submissions to government and other official bodies, commenting in the Christian and secular media and working behind the scenes through the BMA [British Medical Association], in the Royal Colleges and in parliament".

His submission to the parliamentary science and technology committee's inquiry focuses partly on evidence suggesting an abortion increases the risk that a woman's subsequent pregnancies will be premature.