Two Croydon MPs have defended their decision to support a bill making them exempt from the Freedom of Information Act - saying it is for the benefit of their constituents.

The private members' bill would stop letters between constituents and MPs from being made public and would also end the compulsory legal requirement for MPs to disclose their expenses, including such details as how much they claim for travel or pay their secretary.

But the move has been heavily criticised because MPs could have asked the information commissioner to clarify whether their private correspondence was covered by data protection law.

Instead dozens voted for a bill which could restrict the press and the public's ability to scrutinise the spiralling cost of MPs' expenses.

Malcolm Wicks, MP for Croydon North, and Andrew Pelling, MP for Croydon Central, voted to exclude themselves from the act, which was introduced in 2000 to give the public unrestricted access to information held by public authorities, at the House of Commons on Friday. Croydon South MP Richard Ottaway was away so did not vote, but agreed he would have supported it.

He said: "It is a restriction of the Freedom of Information Act but it's done for good reasons because it will protect my constituents. When they write to me they do it in confidence, but the situation at the moment is that these letters can be revealed to the public, something they haven't agreed to. It is this loophole we want to close.

"It's a consequence that it will cover things like travel expenses but we have said that we will voluntarily continue to publish these. Some people would also like me to share details of my secretary's wage but that is a matter for me and her, not public consideration."

Mr Wicks echoed Mr Ottaway's stance. He said: "This is about privacy and confidentiality. My constituents who seek my support on many sensitive issues need to be sure that my letters on their behalf remain private.

"The Speaker of the House of Commons has confirmed that details of MPs' expenses will continue to be published. That is clear and that is right."

The legislation was passed by 71 MPs and will now go the House of Lords where it could become law later this year.

Mr Pelling, whose parliamentary staff include his second wife, Lucy, also agreed that the main purpose of the bill was to protect his constituents.

He said: "I voted to protect Croydon people who write to me about their personal problems from having this information getting into the grubby hands of the local newspapers."

Commenting on the bill, Croydon Guardian assistant editor Danny Brierley said: "I and many others regard the issue of protecting constituents' correspondence to be a flimsy excuse for a bill which would also conveniently make it more difficult for newspapers to tell voters how much public money their Westminster representatives are trousering each year."

The bill will now be passed to the House of Lords before being sent back to the lower house for final approval.