Edward Snowden: Britain issues global warning to airlines not to let CIA leaker board a flight to the UK

Airlines around the world have been warned by the British government not to allow CIA whistle-blower Edward Snowden to board any flights to the UK.

The global alert has been issued to carriers warning the former US intelligence worker, who leaked details of the controversial Prism web spy programme, ‘is highly likely to be refused entry to the UK’.

It marks a major escalation in Britain’s involvement in the snooping scandal, after Foreign Secretary William Hague repeatedly refused to comment on the leaks.

Whistleblower: Edward Snowden, a 29-year-old former CIA technical assistant, claims Britain's GCHQ compiled 197 dossiers on UK citizens based on information from the US spying project Prism

Alert: The UK Home Office issued this warning to airlines that Mr Snowden would be refused entry to Britain

The warning to airlines was made on a Home Office letterhead dated on Monday, the Associated Press reported. The document is thought to be genuine but the Home Office refused to comment.

Mr Snowden triggered shockwaves across the globe by handing over top-secret files from the US National Security Agency (NSA).

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The FBI vowed to hunt down Snowden as U.S. intelligence officials warned he may be attempting to defect to China with a trove of America's most sensitive secrets.

The 29-year-old whistleblower, who earned £130,000 a year ($200,000), exposed chilling details of how the covert agency, based in Maryland, gathers private information from people around the world – including in Britain – using a programme called Prism.

America's National Security Agency and the FBI are said to have easy access to data held by nine of the world’s top internet companies, including Google, Facebook, Microsoft and Skype.

Warning: Bangkok Airways said it received the letter from the Airports of Thailand Pcl on Thursday

Everyday device: Mr Snowden used a humble thumb drive (left) to take top secret documents from a NSA facility in Hawaii

Mr Snowden claims British spies at Cheltenham-based GCHQ compiled dossiers from phone and web data gathered by the US's controversial Prism programme.

It would illegal for British security services at GCHQ to ask the US for data obtained through the programme, but it is alleged that it has received data from the Prism programme since 2010.

In the Commons this week Mr Hague repeatedly refused to comment on the leaks specifically and did not refer to Mr Snowden directly.

But the British government is keen to avoid a repeat of the global embarrassment when Wikileaks founder Julian Assange moved to Britain after revealing US secrets.

The British government will be keen to avoid a repeat of Wikileaks founder Julian Assange who has spent a year holed up in the Ecuadorian Embassy in London fighting extradition to Sweden

He is now holed up in the Ecuadorian embassy in London, after seeking asylum to avoid extradition to Sweden on allegations of sex offences.

Mr Snowden fled the US for Hong Kong after smuggling highly classified files out from the National Security Agency with a humble computer thumb drive, according to the Los Angeles Times.

The Snowden alert to airlines not to let him fly to Britain emerged after a letter was photographed at a Thai airport.

It was was issued by the Risk and Liaison Overseas Network which is part of the UK Border Agency monitoring people who try to enter Britain illegally.

It imposes fines on carriers who bring any passenger to the UK without the proper documents or against instructions from the British government.

The letter was titled 'RALON Carrier Alert 15/13 and referred to: Individual who is highly likely to be refused entry if arriving in the United Kingdom.'

It features a photograph of Mr Snowden, his date of birth, passport number and status as a US citizen.

It added: 'If this individual attempts to travel the UK: Carriers should deny boarding.

'This individual is highly likely to be refused entry to the UK and the carrier may be liable to costs relating to the individual's detention and removal.'

'Carrier alerts' are issued when the U.K. government wants to deny entry to people who don't normally need visas to enter the country, or already have visas but something has happened since they were issued, said the diplomat.

Sometimes convicted sex offenders are denied entry into the UK in this way.

Vanished: A real estate sign stands in front of a home where Edward Snowden apparently lived with his girlfriend in Hawaii. Snowden said he was ill and requested leave without pay, according to sources

A Bangkok Airways officer said the airline was notified on Thursday about the alert by the Airports of Thailand, Pcl., which operates national airports throughout the country. She said the notice was not intended to be seen by the public.

The officer spoke on the condition of anonymity because she was not authorized to give the information to the media.

It was not clear if other countries have posted similar documents.

A Home Office spokesman said: 'We do not routinely comment on individual cases.'