Britain is braced for a diplomatic row after a senior Israeli politician warned that she was preparing to travel to the UK, where she faces an arrest warrant for alleged war crimes.

Tzipi Livni, the former Israeli Foreign Minister and now the leader of the Opposition, said that she wanted to test promises by David Miliband, the Foreign Secretary, that he would change the law to ensure that she was not arrested for her role in last year’s Gaza offensive.

In December, a London court agreed to a request by pro-Palestinian groups to issue a warrant over alleged war crimes during the military operation, which took place when she was Foreign Minister. The court rescinded the warrant when it became clear that she was not on British soil.

At the time, Gordon Brown and Mr Miliband pledged to prevent this happening again and the Government has since been considering various ways of changing the law.

One plan would see a ban on arrest warrants for alleged war crimes, while another could give immunity to former ministers.

Ms Livni has set a deadline of February 23, after which she told The Jewish Chronicle that she planned to visit “within weeks”. Any change to the law would be made in the Crime and Security Bill going through Parliament, which is in the committee stage until that date.

Ms Livni said: “I will do this not for me, not for provocation, but for the right of every Israeli to travel freely. I am not going to be restricted by extremists because I fought terror.”

The British system was, she said, “being abused by extremists for political reasons. Belgium and Spain have changed their laws, and the British know that they have to do so”.

Despite a Tory pledge to support the change, a motion against a new law preventing her arrest has gathered 108 backbench signatories.