Theresa May says new extremism analysis unit is compiling list of legal but unacceptable individuals and groups to prevent another Trojan horse scandal

The Home Office is drawing up a blacklist of extremist individuals and organisations with whom the government and public sector should not engage, Theresa May has revealed.

The list of legal but unacceptable organisations is being compiled by a new Home Office “extremism analysis unit”, which is also to develop a counter-entryism strategy to tackle Islamist radicalisation and ensure there is no repeat of the Trojan horse affair in Birmingham schools across the public sector.

In a speech outlining a wishlist of measures and powers to tackle extremism in Britain, the home secretary acknowledged that the work of the new unit had received only cabinet approval so far.

May was put in charge of developing a cross-government extremism strategy last October, but she has so far failed to resolve outstanding problems raised by at least four Conservative cabinet colleagues.

“Chris Grayling wants more clarity on its impact on prisons. Theresa Villiers wants more consultation with Northern Ireland, where extremism is obviously historically a big issue. Eric Pickles wants work to be done on the impact on communities and faiths and Nicky Morgan wants more work done on the role of Ofsted,” said a Westminster source.

Instead, the home secretary outlined a list of measures a majority Conservative government would introduce, including closure orders for premises being used by extremists, banning orders, and a review of the impact of sharia law in Britain. The package would include a positive campaign to promote British values.

May said the new extremism analysis unit “will help us to develop a new engagement policy – which will set out clearly for the first time with which individuals and organisations the government and public sector should engage and should not engage”.

She added: “This will make sure nobody unwittingly lends legitimacy or credibility to extremists or extremist organisations, and will make it very clear that government should engage with people directly and through their elected representatives – not just through often self-appointed and unrepresentative community leaders.”

She said it was known from the Trojan horse affair in Birmingham schools that extremists use entryist tactics to infiltrate legitimate organisations to promote their own agendas.

“The counter-entryism strategy will ensure that government, the public sector and civil society as a whole will be more resilient against this danger,” the home secretary said in a speech in Westminster.

The move goes far beyond current powers to ban violent extremist and terrorist organisations and paves the way for a range of non-violent legal organisations to be put on a blacklist and boycotted by the government.

David Cameron, for example, has promised for the last five years to ban the non-violent radical Islamist organisation Hizb ut-Tahrir but it has failed to meet the legal criteria to be banned.

The Home Office defines extremism as “vocal or active opposition to fundamental British values including democracy, the rule of law, individual liberty and mutual respect and tolerance of different faiths and beliefs. We also include in our definition of extremism calls for the death of members of armed forces whether in this country or overseas”.

A recent Home Office consultation produced many comments that a much tighter definition was needed and such vague terms could catch a wide range of organisations. Those blacklisted would be likely to mount legal challenges to the decision.

In outlining her list of possible new measures that a majority Conservative government would introduce, May revived the idea of closing down “extremist” mosques, new “extremism officers” in prisons, a review of how Sharia courts impact in England and Wales, a review of citizenship laws to ensure respect for British values, and a review of unregulated “supplementary” schools.

The home secretary called for a new partnership to defeat the extremists. “To those who do not want to join this new partnership, to those who choose consciously to reject our values and the basic principles of our society, the message is equally clear: the game is up. We will no longer tolerate your behaviour.”

Yvette Cooper, the shadow home secretary, said: “Everyone other than the extremists agree that we should robustly defend and actively promote the pluralistic values our society rightly holds in esteem.

“But it isn’t enough for the home secretary to say it, she needs to act.

“We need to work in as many communities as possible, throughout the UK, to support civil society and defeat extremism.

“And we should never tie the hands of our agencies and the police in confronting dangerous, violent extremists. The government’s record is one of making that harder, not easier.”