French President Francois Hollande dealt a blow Friday to Prime Minister David Cameron's hopes of renegotiating Britain's membership of the EU before a referendum in 2017, saying treaty change was "not a priority".

At an Anglo-French summit held at an airbase in Oxfordshire, west of London, Hollande indicated he might be open to treaty change in the future to ensure the eurozone was "better coordinated".

But he noted that any major treaty change could require a referendum in France and said: "We feel that revising the treaty is not a priority for the time being."

Under pressure from eurosceptics in his Conservative party, Cameron has promised to renegotiate Britain's position in the EU and put the new deal to a referendum after the next election in 2015.

Hollande told a joint press conference that he "perfectly respected" Britain's right to hold a vote, but said: "We can't impose the British choice on Europe."

Cameron said he remained optimistic of achieving the changes he wanted and British officials say the fact France is even considering treaty change is progress.

The prime minister said: "My position absolutely remains that we want to see those changes, we want that renegotiation.

"That renegotiation will involve elements of treaty change, and then there will be a referendum in Britain before the end of 2017."

He later revealed he is prepared to invoke a rarely-used law in order to force through parliament a bill guaranteeing an "in/out" referendum in Britain by 2017, after the upper House of Lords killed off legislation backed by his Conservatives.

Cameron said his party will reintroduce the bill once the next parliamentary session begins in May -- and he pledged to invoke the Parliament Act, which enforces the supremacy of the lower House of Commons, if it is blocked by the Lords again.

Hollande and Cameron continued their debate about EU reform during a "convivial" lunch at the nearby Swan Inn, a riverside pub dating back to 1885 which has featured in hit TV series "Downton Abbey", British officials said.

Despite their political differences, the two leaders used their first Anglo-French summit since Hollande's election in 2012 to further cement bilateral cooperation on defence, nuclear energy and space exploration.

The most uncomfortable moment came when a British journalist asked about Hollande's recent separation from his partner Valerie Trierweiler following media reports that he was having an affair with an actress.

"Do you think your private life has made France an international joke, are you still having an affair with Julie Gayet and do you wish she was here?" the reporter asked.

To which Hollande replied: "I will not answer."

Cementing defence ties

Hollande and Cameron disagree on an EU treaty but sought to emphasise their shared goals to improve growth, create jobs and build a more "efficient" Europe.

The Conservative prime minister praised the Socialist president's recent moves to boost the struggling French economy by cutting business taxes and reducing red tape, saying this was "the right way to boost investment and create jobs".

Cameron also praised the Frenchman's "courageous and determined leadership" in Mali and the Central African Republic, promising further logistical support from Britain for the latter mission.

The summit was held at the Royal Air Force (RAF) base at Brize Norton, the base for British C-17 transport planes helping with the French operations in Africa.

The two leaders braved the biting cold to inspect British and French military kit at the base.

In 2010, Britain and France signed a landmark agreement on defence and security cooperation, and on Friday they announced further progress.

In the shadow of a parked RAF A330 Voyager plane, ministers signed agreements to jointly purchase anti-ship missiles for use on naval helicopters and to launch a feasibility study into jointly producing an armed drone.

Claire Chick, head of defence at the Franco-British Council think tank, said there was no sign that London and Paris's political arguments were disrupting their pragmatic partnership on defence.

"The relationship is in difficulty but their defence partnership is safe from any misunderstanding," she told AFP.