By Alasdair Sandford
BBC News, Paris
The French interior minister has described the terrorist threat against his country as "high and permanent".
Nicolas Sarkozy also talked about his tough line on immigration
Nicolas Sarkozy was speaking before a meeting on Wednesday of European Union interior ministers in London in the wake of last week's security alert.
He defended tighter measures at French airports where all hand baggage is now searched for certain flights.
Mr Sarkozy said Wednesday's meeting might seek to harmonise the European response to the threat.
This was the French interior minister's first major interview since Britain said last week it had foiled a terrorist attack.
He also defended his government's policy on immigration.
Speaking on one of French television's main evening news programmes, Mr Sarkozy said the British intelligence services had passed on precise and material information relating to the plot to blow up airliners.
All hand baggage is now searched on flights from France to Britain, the United States and Israel.
Mr Sarkozy said there was no question that France would lower its guard.
"I must be careful with my vocabulary, but it has to be specific and understood: the terrorist threat to France is high and permanent," he told the France 2 channel.
"Specialised French anti-terrorist services are taking what happened in Britain very seriously," he said after meeting top police and intelligence officials.
Mr Sarkozy said he hoped Wednesday's meeting in London with his British counterpart John Reid and other EU ministers would lead to a unified response to the terrorist threat.
On the subject of immigration, the interior minister confirmed that thousands of families would be forced to return to their countries of origin if their applications to stay in France were rejected.
Denying accusations of organising a "child hunt", he said there had been nearly 30,000 claims concerning illegal immigrants with children in French schools.
"You saw what happened in the suburbs, one sees the difficulty of France's integration system," he said, apparently referring to the riots which erupted in parts of French towns last autumn.
"What's the reason for this? The reason is that our immigration policy has not been mastered.
"Just coming to France does not give you the right to stay in France."