Birmingham MP John Hemming has won his battle against lawyers who tried to gag his criticisms of a property developer, following a long-running row over a shopping centre in Yardley.

An inquiry found that leading London law firm Withers LLP were wrong to try to stop Mr Hemming (Lib Dem Yardley) speaking out in Parliament.

It followed a row between Mr Hemming and their client Jeremy Knight-Adams over the future of the Swan Shopping Centre in Yardley, where supermarket giant Tesco hopes to build a new store.

Withers LLP was in breach of the 1688 Bill of Rights, which guarantees that MPs must be allowed to speak freely in the House of Commons without fear of legal action, a Commons inquiry found.

But no action will be taken against the law firm, because it has already issued an apology to Mr Hemming and to the entire House of Commons.

In theory, anyone found to be guilty of trying to gag Parliament - which would mean they are “in contempt of Parliament” - can be hauled into cells built into the Big Ben clock tower.

The row began when Mr Hemming told Withers he planned to make a Commons speech attacking Mr Knight-Adams, who owns some land at the Swan shopping centre.

The developer had refused to sell it to Tesco, delaying the supermarket giant’s plans to build a new store on the site, which is currently derelict.

Mr Knight-Adams argued that his alternative proposals for the site, which included additional shops, bars and restaurants, offices and community facilities, would create more jobs than Tesco’s proposals.

But Mr Hemming warned Withers LLP in August that he intended to make a speech in Parliament “in which he would refer to ‘behaviour’ of one of the firm’s clients which, in his view, was ‘a spoiling tactic’ and amounted to ‘bullying tactics’”, the Commons inquiry said.

In response, Withers LLP threatened to sue Mr Hemming over a leaflet he had issued in his Yardley constituency, which they said had attacked Mr Knight-Adams, unless he promised not to repeat the criticisms in the House of Commons.

A report published by the inquiry, chaired by former Foreign Secretary Malcolm Rifkind, said: “The evidence in this case is very clear and in our view the conclusion is no less clear. We conclude that Withers LLP were in contempt of the House.”

It added: “We are surprised that a form of the standing of Withers LLP should have taken so long to understand the scope of Parliamentary privilege.”

But the committee decided to take no further action after Withers sent a letter saying the firm “would like unreservedly to apologise to the House and to Mr Hemming.”

Although MPs are subject to the same laws as everyone else when they speak or publish leaflets outside the Commons, they are protected in Parliament itself by article 9 of the 1688 Bill of Rights, which states: “The Freedome of Speech and Debates or Proceedings in Parlyament ought not to be impeached or questioned in any Court or Place out of Parlyament.”

Tesco’s plans to build a new store on the Sawn site are likely to go ahead after an attempt to compulsorily purchase the land needed was approved by the Government.