Counter-terror chiefs yet to use exclusion powers on returning fighters
Powers to control the return of Britons suspected of involvement in terrorist activities abroad are yet to be used, almost two years after they were introduced.
Temporary Exclusion Orders (TEOs) were unveiled amid warnings over the potential danger posed by battle-hardened extremists re-entering the country following the rise of Islamic State (IS).
They aim to disrupt the return of UK nationals radicalised while fighting overseas and passed into law in February 2015.
But it has emerged that no TEOs have been issued so far - sparking calls for ministers to explain why they have not been deployed.
The Home Office told the Press Association the Government remains ready to use the powers.
The question of how to manage the return of those who have fought alongside extremist groups such as IS - also known as Isil - has emerged as a challenge for counter-terrorism agencies.
Around 850 UK-linked individuals of "national security concern" have travelled to engage with the Syrian conflict, with just under half thought to have come back.
The disclosure on TEOs was contained in a report by Professor Emeritus Clive Walker QC, a senior special adviser to terror laws watchdog David Anderson QC.
Several practical difficulties may be standing in the way of effective enforcement, suggested the paper on "foreign terrorist fighters" (FTFs) which was published last month.
It said: "One is that some would-be FTFs will actually return on the terms of the sending state by way of deportation. The second problem is the complexity of detection, at least until arrival at a UK port."
TEOs were created to disrupt and control the return of British citizens believed to have engaged in terrorism-related activity abroad.
They make it unlawful for the individual to come back without engaging with UK authorities.
The orders, which can remain in force for up to two years, are supported by cancellation of the subject's travel documents and inclusion of their details on watchlists. Requirements can then be placed on the suspect once they return to the UK.
There were already powers to block foreign or dual nationals from travelling to Britain from conflict areas but TEOs were devised to address a gap in the measures available for UK citizens.
A government factsheet published in December 2014 said they would provide a "valuable operational capability".
Labour MP Yvette Cooper, chairwoman of the Commons Home Affairs Committee, said: "Given that the threat from Isil remains extremely serious, and that the Government said these measures were so crucial, they need to explain why none have been used after all.
"Is it because they believe the threat has changed or is it because in practice the police and security services don't believe they make any difference?"
Shashank Joshi, senior research fellow at security think-tank the Royal United Services Institute, said it was hard to say why no TEOs have been issued.
He said: "It may have been easier to rely on existing mechanisms to monitor and influence returnees.
"Indeed, the threat of applying a TEO may have helped to influence potential returnees, along the lines of 'co-operate with us, or we will impose a TEO'."
A Home Office spokeswoman said: "It is right that use of this power is considered on a case-by-case basis.
"The power continues to be one of a number of tools available to law enforcement and security agencies to manage the threat posed by individuals suspected of terrorism-related activities overseas, and we remain ready to use it."
Prof Walker's study - included as a guest chapter in Mr Anderson's annual report - said rates of recruitment and travel have been falling from a peak in 2014 but found the threat posed by FTFs remains "clear and present".
The threat level for international terrorism in the UK stands at severe, meaning an attack is "highly likely". Security services and counter-terrorism units have foiled at least 10 attacks in the past two years.