The gangs, from Serbia, Croatia and the Czech Republic, have held meetings at which they agreed to put aside traditional rivalries for the duration of the tournament.

The Sunday Times has learnt of a meeting held two months ago in Serbia, involving six Czech skinheads and the Delije, notoriously violent supporters of Red Star Belgrade. Two weeks later they met a group of hooligans from Croatia.

Fifteen years ago a pitched battle in a football stadium between Red Star fans and a rival Croatian club was one of the sparks that ignited the Balkan wars.

One of the Serbian organisers, Dragan Banovic, explained: “Germany will be one big battleground this summer. This is an opportunity for our groups to shout our message and to know people will hear it.”

Banovic, a former paramilitary who fought in Bosnia alongside Arkan, the Serbian war criminal assassinated in 2000, added: “For the time of the World Cup, traditional rivalries will be forgotten. I will be able to stand alongside others from Zagreb and Split, from Prague, Rome and Milan to shout with one voice because we all feel the same.

“There will be many more in Germany who will have sympathy with us and we think we will be able to cause many problems for the police. Our targets are the black players and those who follow them. The black players from England will be a good target for us because they will react to what we shout and to the banners we will be carrying. We will be throwing more than bananas at them.”

The thugs say they will not be deterred by measures intended to prevent them from buying tickets, and will fight outside the stadiums. They plan to link up with like-minded hooligans from Italy’s notorious extremist groups to create “Ultras United”.

At a meeting held in London last month, European police chiefs discussed how to prevent fascist groups from targeting African teams and black members of the England squad, such as Rio Ferdinand, Sol Campbell and Ledley King.

Two other England players, Ashley Cole and Shaun Wright-Phillips, were the victims of monkey chants a year ago during a friendly game against Spain. The Spanish footballing authorities were forced to apologise for the behaviour of spectators in Madrid. Piara Power, national co-ordinator of the Kick It Out anti-racism campaign, said: “In some places in eastern Europe, whenever there is a Jewish or black player on the field of play, they are constantly abused.”

Despite the relatively low levels of disorder at Euro 2004, held in Portugal, and the 2002 World Cup in South Korea and Japan, senior officers are worried that Germany will be harder to police. It has open borders with nine neighbouring countries.

More than 3,200 England fans identified as troublemakers will be stranded at home under banning orders that require them to surrender their passports and report to local police stations on match days.

One police source, with responsibility for monitoring Europe-wide hooliganism, said peaceful England fans might now be prime targets for troublemakers seeking to test their prowess.

Superintendent Andreas Morbach, joint head of the German police Landeskriminalamt football intelligence unit, based in Düsseldorf, said: “We have a big potential for violence from our supporters. They live here, they know how to act and they are now prepared.”

Morbach said that 9,000-10,000 German hooligans could become violent, depending on the provocation. The German police are concerned that visiting England and Holland fans will be wearing replica plastic Nazi storm-trooper helmets in the colours of their country.

A Dutch firm will this week start production of helmets bearing the flag of St George and the slogan “No One Likes Us” usually chanted by Millwall fans.

Florian Van Laar, joint head of the company producing the helmets, said: “It is meant as a joke. The Germans are not meant to have a sense of humour, but we Dutch do have one. We are getting calls from all over Europe, even from those who have not even qualified for the tournament. After all, the Germans invaded most countries, so people want to wear these. If they think this is provocation, the only thing I can say is, now you know how we feel.”

Morbach said: “It is not nice to have a sports event compared to war. We try to use as our theme for this cup, ‘It’s time to make friends’.”