One of Britain's most wanted fugitives has been arrested in Romania.

Shane O'Brien, 31, is suspected of the murder of 21-year-old Josh Hanson, who was stabbed to death in a bar in Hillingdon, west London, in 2015.

He fled in the wake of his death and was put on Interpol's worldwide most wanted list with a £50,000 reward offered for information leading to his arrest and prosecution.

Josh Hanson was killed in an unprovoked knife attack in 2015. Credit: Met Police/PA

Scotland Yard said O'Brien was detained by authorities in Romania on Saturday after the force issued a European arrest warrant.

Extradition proceedings will begin to bring him back to the UK.

The Metropolitan Police said Mr Hanson's family have been kept up to date with developments.

O'Brien grew his beard and hair long while on the run. Credit: Met Police/PA

O’Brien fled the country in a private jet immediately afterwards and had stayed one step ahead of the authorities ever since, with help from criminal contacts.

Reacting to the news on Twitter, the Josh Hanson Trust, a charity set up in the wake of his death, sent a message of thanks to the officer investigating the case, DCI Noel McHugh, followed by "Love you Josh".

Another tweet read: "Today on the 23rd of March 2019 and after 3 and a half years of waiting today is Josh's day."

Mr Hanson's mother, Tracey, spoke in December last year of her frustration at the length of time it was taking to catch up with O'Brien.

“I can’t believe he hasn’t been arrested. I can’t believe he left the country in a private jet, just flew out of the country. How are the police so behind his every move?" she said.

It is believed O'Brien spent time in the Netherlands, Dubai and at least seven months in Prague, where he may have had a string of affairs with women and spent time in boxing clubs, gyms and nightclubs.

Police photos taken at the time show he had changed his appearance, having longer hair and a beard, and a new, large tattoo of an owl holding a skull that covers a large portion of his back.

This was to cover up a distinctive tattoo that he had previously, that said "Shannon 15-04-06".

A new tattoo on the back of fugitive Shane O'Brien. Credit: Met Police/PA

Ian Cruxton, the National Crime Agency's (NCA's) head of international operations, said: "O'Brien has spent several years looking over his shoulder as he has been at the centre of an extensive operation to track him down.

"I'm delighted that the pressure brought to bear by this has finally resulted in him being captured as a result of close working with the Romanian authorities.

"I hope his arrest offers some comfort to the family and friends of Josh Hanson."