Downing Street has confirmed that the prime minister will sign the European Union Reform treaty on Thursday.

However Number 10 would not say whether Gordon Brown will do so in public.

There has been some doubt about whether Brown would be able to travel in time for the signing ceremony at this week's Lisbon EU Council meeting, due to his commitment to appear before the Commons liaison committee on Thursday morning.

But the prime minister's spokesman told reporters on Tuesday that Brown would be attending the summit, although not in time for the official ceremony.

Downing Street said foreign secretary David Miliband will be attending the ceremony while Brown will sign the controversial document later in the day.

However Number 10 would not say whether this will be done behind closed doors.

"People will not be in any doubt that he has signed the treaty," was all the spokesman would say.

Shadow foreign secretary William Hague said: "Some people say Gordon Brown's problems are that he isn’t decisive and he lacks political courage.

"He couldn't have done more to confirm that than this ridiculous fudge. He's dithered over it for a week and now he decided that he'll sign this treaty but he doesn't have the guts to do it in public. His excuses fool no one: he must stop treating people like fools.

"If he backs the renamed EU constitution so much that he's ready to break his manifesto promise, he should at least have the courage to be photographed doing it.

"If he's ashamed of signing this treaty then why doesn't he honour his election promise and let the British people have their say?"