Pro-life charity workers attend the Speaker's private reception

Members of the pro-life charity lobbying MPs to vote against the Human Fertilisation and Embryology Bill attended a private reception hosted by the Speaker, Michael Martin, it was claimed yesterday.

Research assistants funded by Christian Action, Research and Education (Care), along with other Christian activists, were entertained at the House of Commons apartments overlooking the Thames last summer, according to insiders.

The link between Mr Martin, a Catholic, and the charity leading opposition to the Embryology Bill will heighten concerns about lobbying in Parliament.

The Charity Commission was still examining Care's activities, which includes the charity's funding of up to 12 researchers in the offices of MPs in the run-up to free Commons votes on the Bill later this year. Under law, charities "must not give support or funding to a political party, nor to a candidate or politician". There is no suggestion of wrongdoing whatsoever on the part of Mr Martin.

New claims also emerged that material supplied by Care urging MPs and peers to vote against the Bill has been sent through Westminster's internal post and email system – in apparent breach of parliamentary rules. Official guidance on using free internal mail states: "Since lobbying is a political activity, this charge cannot be borne by Parliament and ultimately the taxpayer."

One peer said she had received dozens of letters, including Care literature, urging her to vote against the Bill as it passed through the Lords earlier this year.

"There were no stamps on the envelopes, but some of the letters claimed to be from ordinary members of the public," she said. "It concerns me that it appears the system is being abused in this way."

The Bill would make it easier for scientists to create human-animal hybrid embryos for medical research, change rules on the need for a father for IVF treatment and is expected to carry a vote on the time limit for abortion. MPs have been given a free vote on the most contentious clauses, following pressure from the Catholic Church and other religious bodies.

Labour MP Paul Flynn, a member of the Public Administration Select Committee which is conducting an inquiry into political campaigning by charities, said: "You cannot stop people attending the Speaker's receptions, but it does show how we are infiltrated on all sides by various groups."

A spokesman for Care said: "Interns are not allowed to lobby on Bills. We recognise it would be improper." The spokesman added that he had no evidence that material had been sent through the internal mail, but it was possible "MPs had done so on behalf of their sponsor".