The tuna sandwich has been the staple of the snatched office lunch for a generation.

But our favourite fish filling could soon vanish from the high street.

Sandwich chain Pret a Manger yesterday announced it is scrapping its tuna and cucumber sandwiches - and taking premium bluefin tuna out of its sushi boxes - amid concerns about overfishing.

Other stores and sandwich chains are under pressure to follow suit.

Pret founder Julian Metcalfe made the decision after being horrified by a hard-hitting new documentary on the state of the world's oceans.

The End of the Line, which premieres today at 50 cinemas, shows how intensive fishing is destroying the oceans and warns that most of the seafood we eat will have vanished within 40 years.

One of the first to go will be bluefin tuna - the expensive delicacy favoured by sushi lovers.

New evidence suggests it has been taken from the Atlantic and Mediterranean so quickly in the last few years that stocks are on the verge of collapsing.

After a private screening of the film, Mr Metcalfe announced that Pret a Manger and its sister store Itsu would no longer sell bluefin tuna or sandwiches made with canned tuna.

In an email to the film's producers, he said: 'Much as a result of your film, we took tuna out of Pret sushi entirely. No tuna in the box at all, so more in the sea where they belong.'

He added: 'We no longer sell the tuna and cucumber sandwich.'