A private members’ bill to exempt MPs and peers from freedom of information laws has been slammed as “inconsistent and unprincipled” – by a group of MPs.

More than 50 have put their names to an Early Day Motion, saying that it would undermine Parliament’s ability to have any authority or set any example on issues of accountability, openness or transparency in Government and public life.

The parliamentary petition was tabled by the Liberal Democrats’ Simon Hughes, MP for North Southwark and Bermondsey, after the private members’ bill passed through the House of Commons.

It secured its third reading – which will be in the House of Lords – by 96 votes to 25, a majority of 71.

The legislation was introduced by Tory former chief whip David Maclean, and supporters say it will protect the confidentiality of correspondence between constituents and MPs.

But the EDM says this argument is not based on evidence, and should only be introduced if careful and considered advice confirms a need for changes to the law.

The full EDM reads: That this House notes the Third Reading of the Freedom of Information (Amendment) Bill on 18th May; believes that it is inconsistent and unprincipled to seek to exempt the affairs of the House of Commons and House of Lords from the obligations of the Freedom of Information legislation, which applies to all other public authorities and only took effect in 2005; believes that the passage into law of the Freedom of Information (Amendment) Bill would fundamentally undermine respect for both Houses of Parliament, all the Houses’ hon. Members and officers, and most importantly Parliament’s ability to have any authority or set any example on issues of accountability, openness or transparency in Government and public life; and believes that the argument that more laws are needed to protect confidentiality of correspondence between hon. Members and those whom they represent is not made out on the evidence, should only be introduced if careful and considered advice confirms an agreed need for changes to the law, and should not be used as an excuse, justification or distraction for a major attack on the rights of British citizens to hold to account all hon. Members of Parliament passing laws in their name.

MPs who have already signed include Glenda Jackson, Lembit Opik, George Galloway, Nick Clegg and Don Foster.

A separate petition opposing the move has also been launched at http://petitions.pm.gov.uk/foiparliament/.