Scuffles broke out in Manchester on Sunday as police and bodyguards escorted the National Front leader's car past protesters as he left a news conference by the far-right British National Party.
Le Pen was in Britain at the invitation of BNP leader Nick Griffin to help launch the British party's campaign for the June European elections.
Le Pen, who was last month fined for inciting racial hatred in Paris, told reporters France risked being "submerged" by immigrants.
"In France, we had 10 million immigrants in the past 30 years. If this is not stopped the population risks being submerged by these great invasions," he said, speaking in French.
Local politicians had condemned Le Pen's visit to Manchester, a few kilometres from the scene of violent race riots in the town of Oldham in 2001.
Protesters pelted Le Pen's car with
eggs and rubbish
Home Secretary David Blunkett had warned Le Pen he faced arrest if he provoked racial tension during his visit.
"I'd rather Mr Le Pen wasn't here and I'd rather the British National Party didn't exist in our country," he told BBC television.
Later on Sunday Le Pen attended a dinner with BNP supporters in rural Wales in a successful attempt to escape further disruption from protesters.
Police blocked off the narrow lanes leading to the dinner, held in a marquee decorated with red, white and blue balloons near the Welsh village of Llandrinio.
About 200 BNP supporters, of all ages and in formal black tie dress stood up and cheered as Le Pen and Griffin entered with their arms around each other's shoulders.
With mounted police patrolling outside the marquee, Le Pen spoke to repeated applause, as he hailed the solidarity between French and British nationalists.
Unlike Le Pen's National Front, which gained 16% of the vote in France's recent regional elections, the BNP remains on the fringe of British politics, but has had some success in local elections.