By Humphrey Hawksley BBC correspondent in Frankfurt

Five men with suspected links to al-Qaeda are due to go on trial on Tuesday in Frankfurt, accused of planning an attack on Strasbourg - the seat of the European Parliament.

The group was arrested in December 2000, long before the terror attacks on America, and since then, the whole fabric of the European intelligence and security operation has been overhauled.

We're crossing borders and pooling our intelligence, whereas before, everything was done on a bilateral basis

Europol chief analyst Simon Robertson

The focal point is Europol, housed in a former Gestapo headquarters in The Hague, Holland. It was only set up in 1999, but is becoming the biggest intelligence gathering centre in Europe.

"Here we have a link into some synthetic drugs," says Simon Robertson, Head of Analysis for Europol, pointing to a huge wall chart.

"That may well be a financing operation through drug dealing activities, and up here, in Britain, we have another area which is also involved in drugs.

"So we're crossing borders and pooling our intelligence, whereas before, everything was done on a bilateral basis."

Sharing information

He pointed to another section of the chart in Spain. "And here we've got a weaker link we need to firm up on and that's where intelligence gathering is important."

Member states will have to expand Europol's role so that it becomes the nucleus of a European force

German Federal Police Director Leo Schuster

German police say that as the trial gets underway in Frankfurt, they have not identified any specific threat to attack the proceedings.

Europol, however, is on an increased alert for suicide or biological terror attacks. They may not be connected to the trial itself - but could be prompted by that, or violence in the Middle East.

Since 11 September, files at the German Federal Police headquarters are shared with Europol as a matter of policy, and with the US.

Europol has to request and cannot demand intelligence, but instructions have gone out that a single police force or department should no longer sit on information as before.

Joint strategy

The long-term result is expected to be a pan-European operation with a massive data base which will lead to Europol having extensive de facto powers.

Europol is becoming the biggest intelligence gathering body in Europe

"Member states will have to expand Europol's role so that it will become the nucleus of a European force," said Leo Schuster, Director of the German Federal Police.

"That would include the new eastern European members as well. Then we'll all have to work even more closely together to come up with joint security strategy."

Past mistakes

One glaring example of how things did not work properly, is how the Taleban ran an unofficial embassy before 11 September from cheap offices rented in Frankfurt's red light district.

They also had cells in Milan, Hamburg and London - just to name a few.

You could turn up in Frankfurt if you wanted to get a visa for Taleban Afghanistan, travel advice or sign up for an al-Qaeda training camp.

But now, with the new security apparatus being put up throughout Europe, that sort of thing should never be able to happen again.