A protester who has held an anti-war vigil opposite Parliament for four years has won the right to challenge new laws which threaten to evict him.
Mr Haw has fought off several eviction threats
From 1 August the police will have the power to move Brian Haw, 56, as all protests within a half-mile zone in Westminster must have prior permission.
Three High Court judges began hearing the case immediately and will give their judgment by the end of the week.
Mr Haw, from Worcs, claims he is exempt as his protest pre-dates the new laws.
The measures, part of the Serious Organised Crime and Police Act, effectively ban all spontaneous protests near Parliament.
Mr Haw has been protesting in Parliament Square, surrounded by anti-war placards, since June 2001.
But his position is under threat as anyone who wants to demonstrate within the "exclusion zone", will need police permission or face removal or arrest.
Ahead of Tuesday's hearing Mr Haw said: "The government clearly do not want me as a constant reminder of the immense suffering they are causing the people of Iraq."
Lady Justice Smith, sitting with Mr Justice Simon and Mr Justice McCombe, ruled his case should go to a full hearing and, because of its urgency, should proceed immediately.
Richard Drabble QC, appearing for Mr Haw, said he was seeking a declaration that Mr Haw did not need to apply for authorisation to continue the demonstration he started four years ago.
Mr Drabble said: "At the heart of the case is the proposition that.... it is quite clear that the section [of the law] does not apply to demonstrations which had already started before commencement (of the new Act)."
Nathalie Lieven, appearing for the home secretary, said the new law applied to continuing as well as new demonstrations and described the arguments being put forward by Mr Haw's legal team as "absurd".
Ms Lieven said Mr Haw's display of anti-war banners, placards and flags gave rise to a potential security risk.
"It would be easy to leave items that would cause a serious risk to members of the public and MPs," argued Ms Lieven.
Adam Clemens, appearing for the Commissioner of Police, said Mr Haw was already regularly checked for security purposes, but other people "in the current climate" might seek to take advantage of the relationship they had built up with him.