By Caroline Wyatt BBC News Paris correspondent

Mr Fillon said the result gave the UMP a strong mandate for reform

Dismay and disappointment were clear on the faces of UMP supporters as they watched the results come through.

French President Nicolas Sarkozy's centre-right party may have won an outright majority with 314 seats, but it was far from the "blue tidal wave" or "blue tsunami" predicted by the opinion polls.

Instead, it was a modest victory which gives Mr Sarkozy's party a clear majority in the National Assembly, but a smaller one than it had under former President Jacques Chirac.

But the UMP Prime Minister, Francois Fillon, insisted it was still a clear endorsement of the president's planned policies.

This victory is a reward for the tremendous momentum created by Nicolas Sarkozy UMP leader Francois Fillon

"This victory is a reward for the tremendous momentum created by Nicolas Sarkozy," Mr Fillon told the party faithful.

"We are going to carry out reforms, we are going to engage in renewal, we are going to experiment with new ideas, we are going to enhance the status of work, we are going to encourage talent and innovation, and we are going to free ourselves from the defeatism which is suffocating the Republic."

'Tough election'

However, Mr Fillon's number two, Alain Juppe, was forced to resign from the cabinet after losing his parliamentary seat, which will lead to a cabinet reshuffle this week.

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Some at the UMP blamed the Socialist Party's focus on the government's controversial proposal to raise Value Added Tax for scaring the voters away from handing too much power to the right.

UMP candidate Pierre Lellouche said it had been a long and tough campaign, lasting more than nine months since the start of work on the campaign for last month's presidential election.

"It was a tough election, but the main thing is that the voters have given us a majority to govern and implement reform," he told the BBC. "That is the key thing."

"I am disappointed," admitted one UMP campaigner. "I thought we would have more MPs, but we are still in power."

Socialist relief

Over at the Socialists' headquarters, there was delight and relief.

Ms Royal says she will challenge Mr Hollande to lead the Socialists

They may still be in opposition, but winning 185 seats was the best news the beleaguered party has had for some time.

The party's leader, Francois Hollande, promised that the French left would be an active opposition in the new parliament.

"The blue wave that had been predicted did not take place," he said.

"In the new parliamentary assembly, there will be diversity and pluralism. That's good for the country. Our citizens have brought in a force to face the new power, allowing a balance and a counter-power that is indispensable for a democracy."

Royal split

But it was a separate announcement by his long-term partner, the defeated Socialist presidential candidate, Segolene Royal, that is likely to dominate the debate over the coming days.

Ms Royal announced in an interview on French radio that she and Francois Hollande were no longer a couple.

All couples have their difficulties, and we have had ours... And now we are moving on to a new phase Segolene Royal

They have four children together, and have long been the "golden couple" of the Socialist Party.

The two have been together since they were both at the elite Ecole Nationale d'Administration, which turns out France's top civil servants and politicians. They never married.

"All couples have their difficulties, and we have had ours. And now we are moving on to a new phase," Ms Royal told the France Inter radio station.

The revelations are expanded on in a book to be published by Ms Royal this week, in which she says Mr Hollande had been having an affair and that she had asked him to leave their home.

Leadership challenge

The announcement will end the speculation and rumours that have been sweeping Paris over the past months about the exact state of their partnership, which had clearly been put under strain by disagreements during the presidential election.

Despite the French media's much-vaunted respect for the private lives of politicians, the papers are full of the split-up BBC Europe editor Mark Mardell Read Mark's thoughts in full

Ms Royal complained of a lack of support from the party, while Mr Hollande was occasionally quoted making less-than-supportive remarks or contradicting Ms Royal's policies.

Most embarrassing of all was the moment when Ms Royal's official spokesman was asked during the campaign what her biggest problem was.

"Francois Hollande," he replied and was promptly suspended for a month.

Now, though, the way is clear for Ms Royal to challenge her former partner for his job as leader of the Socialists, a position he has held for the past 10 years.