Eleven Britons have been detained in the Algarve over alleged public order offences.
The group was held by the authorities overnight in an area of the country where thousands of England fans have flocked to watch the national team during their Euro 2004 campaign.
A foreign office spokeswoman said: "Eleven British nationals have been detained. There was a disturbance last night and they have been detained for public disturbance-related matters.
"We are in touch with the authorities and consular assistance will be offered in the normal way."
The trouble comes after England fans in Portugal were praised by local police yesterday as an example to other nations.
A Portuguese national police spokesman said no England supporters were arrested in Lisbon after coach Sven Goran Eriksson's team lost its opening game to tournament favourites France.
In contrast, hooligans went on the rampage across Britain following the 2-1 loss.
Dozens of people were arrested and police came under attack with bricks and bottles and patrol cars were set alight as serious disturbances broke out in town centres as far apart as Croydon, south London, and Wakefield, West Yorkshire.
PA