Gordon Brown will miss the official signing ceremony for the EU reform treaty in Lisbon but will fly to Portugal to meet European leaders, Downing Street said today.
A diary clash with a Commons committee had prompted speculation the prime minister would be forced to withdraw from the treaty signing entirely.
Today Number 10 confirmed Mr Brown will leave London immediately after he finishes giving evidence to the House of Commons liaison committee on Thursday morning.
Mr Brown will arrive in Lisbon in time for lunch with the 27 European heads of government and foreign secretaries.
However, he will miss the formal signing ceremony and photo call, where the UK will be represented by the foreign secretary David Miliband.
Downing Street said: "The prime minister will go to Lisbon but, because of the timing of the liaison committee, he will be unable to make it for the actual signing ceremony.
"However, he will attend some of the lunch with other leaders and he will sign the treaty while he is there. He will also have a meeting with [Portuguese prime minister] Socrates."
Ministers insist past EU treaties have been signed by UK foreign secretaries so the prime minister's presence is "not a particularly significant issue".
The liaison committee announced last week it would call the prime minister to give evidence on Thursday morning.
The prime minister's official spokesman today denied the suggestion the committee had been inflexible, saying he did not recognise that description.
He said: "We have done everything we can to accommodate the PM's travel plans to Lisbon and the liaison committee agreed to move forward its meeting from 10am to 9am so the prime minister could be in Lisbon for as much of the day as possible."
Since Tony Blair's leadership, the liaison committee, which draws together the chairmen of 31 Commons committees, has called the prime minister every six months.
The committee can grill the prime minister on any aspect of government policy and Downing Street said it did not expect the session to last less than a minimum of two hours.