More than 20 people have been arrested during a protest in London in support of Palestine Action, a group which has been banned under UK anti-terrorism laws.

British police arrested over 20 people on suspicion of terrorism offences after they showed support for the newly banned Palestine Action group in London, officials said on Saturday, hours after the proscription came into effect.

The protest group was officially classified as a terrorist organisation from midnight on Saturday after the measure received overwhelming support from MPs and following the failure of a last-minute legal challenge to delay it.