The director of human rights group Liberty has fired a warning shot to the government two days after prime minister Theresa May pledged not to allow ‘activist, left-wing human rights lawyers harangue’ Britain’s armed forces.

In a keynote speech at the Legal Aid Practitioners Group conference in Leeds on Friday, Martha Spurrier said: ‘Just to be absolutely clear, I’m an activist human rights lawyer. We are watching Theresa May, and we are watching Amber Rudd, and Liz Truss, and Michael Fallon, and politicians across the political spectrum, and we will not be cowed - not by your cuts, or by your spin or by your cumbersome computer systems.

‘We are watching you. And if you put one toe out of line we will come down on you like a ton of bricks because we are activist human rights lawyers and that is what we do.’

Earlier in the week, the prime minister and defence secretary Michael Fallon announced much-trailed plans to bring an end to an ‘industry of vexatious claims’ against the armed forces. May told the Conservative party conference the following day that the government would ‘never again - in any future conflict - let those activist left-wing human rights lawyers harangue and harass the bravest of the brave - the men and women of Britain’s armed forces’.

The Doughty Street Chambers associate tenant also used her speech at the LAPG conference to highlight the issue of indefinite administrative detention of immigrants in Britain.

Pointing out that over 30,000 immigrants are detained every year, she said: ’They haven’t broken the law, they’re not serving criminal sentences. The fact of their detention has not been authorised by a judge, and there is a real risk that it will never be authorised by a judge as they stay there. They don’t know how long they are going to be detained for. They are there for the sheer convenience of the state.’ 

She added: ‘One of the things that has struck me most in my first few months of my new job, talking to people who are not lawyers, speaking at party conferences, is there are so many people who don’t even realise that we do this. 

‘There are so many people who have no idea that Britain is the only country in Europe that uses indefinite administrative detention as a form of border control. If they did realise, I think this government might be forced to end it.’

Spurrier said the way detainees - who include pregnant women, children, and those who are mentally ill or physically disabled - are treated ‘is absolutely horrifying’.

Urging practitioners to speak loudly on the issue, Spurrier said: ’I think people might want less immigration, but I don’t think that they want unfair immigration policies. And I don’t think that they want the immigrants here to be treated in a way which completely perverts their right to dignity.’

‘If we start to dismantle the worst edges of this system, then I really think we can move in and start to deal with the rest of it.’