Britain on Friday designated all of Hamas a “terrorist group", warning that its members and those who support the group could face stiff jail terms.
The al-Qassam Brigades, the military wing of the group that rules the Gaza Strip, has been banned in Britain since 2001 but the interior ministry extended the ban to its political entities.
London said last week it was no longer possible to make a distinction, assessing that Hamas "commits, participates in, prepares for and promotes and encourages terrorism".
"Hamas has today become a proscribed terrorist organization in the UK in its entirety following parliament's approval," the Home Office said.
"This means that members of Hamas or those who invite support for the group could be jailed for up to 14 years."
Israel has welcomed the move, which follows similar action by the United States and the European Union.
But Hamas itself has called the UK move "a crime against our Palestinian people and all their history of struggle".
It expressed “shock and dismay” at the British government’s decision and accused the UK of continuing "with its aggression against the Palestinian people.”