As many as 25 MPs from the far-right Alternative for Germany party are to be put under surveillance by Berlin’s domestic spy service after an organisation they belong to was classified as extremist.

The move means that the BfV intelligence service will be able to use the full armour of its spying technologies against up to a third of the AfD’s 89 parliamentarians.

On Wednesday spy chief Thomas Haldenwang announced that the BfV had found Der Flügel (the Wing) to be an extremist organisation that was working against Germany’s democratic order.

While not officially part of the AfD, Der Flügel was set up by the party’s leader in Thuringia, Björn Höcke, and overlaps to a large extent with the party.

Mr Höcke’s name has become a byword in Germany for the resurgence of the far-right due to provocative speeches in which he has condemned the country’s culture of Holocaust remembrance and referred to Islam as an “occupying power” in Germany. He set up Der Flügel in 2015 and has convinced leading AfD figures to appear at its meetings.

Research by Welt am Sonntag newspaper, based on analysis of which AfD MPs have regularly attended Der Flügel meetings and which have signed its declarations, shows that up to 25 MPs are likely to be put under surveillance.

The newspaper notes that its evaluation of who belongs to Der Flügel largely mirrors that of the BfV. At least two of the MPs likely to come under observation could face immediate consequences due to their careers in public service.

MP from Dresden Jens Maier is a qualified judge, while Thomas Seitz MP is a prosecutor. Announcing the decision on Wednesday, Mr Haldenwang warned that public servants, who swear an oath of faith to the constitution, would “run into problems with their employer.”

The AfD, who won a court case against the BfV last year, have announced they will take the spy agency to court again over its decision.

“It has become clear that the BfV under its new chief is primarily interested in pursuing political goals, this has nothing to do with protecting the constitution,” said AfD MP Roland Hartwig.