Tell a friend from Leeds that you are from "Bratford" and he'll tell you you're wrong.

"No, it's 'Bradford' - with a 'd'," he'll say. And you'll both be right.

Born-and-bred Bradfordians traditionally speak a different dialect to Leeds people and that "t" is a real giveaway. It's only outsiders who say "Bra-d-ford", with the emphasis on the "d". But soon it won't matter because, language experts warn, you and your Leeds pal will be speaking identical English.

Dialects could soon disappear altogether as accents in urban areas merge into one. Experts say it's because young people are going further afield for work and pleasure.

But the local "language" has been saved for posterity on a website. In the biggest compilation of authentic northern speech ever compiled, the British Library sound archive site now contains genuine Bradford voices.

Jonathan Robinson, Curator of English Accents and Dialects at the British Library Sound Archive, said: "Accents are changing all the time and always have but what's happening now is that urban accents are spreading out and the difference between Leeds and Bradford is only most obvious in older speakers."

Bradford College languages expert Bob Carlisle said: "When I was at school in Bradford in the sixties we could tell who came from Denholme, Bradford Moor or Greengates by the way they spoke - they had words of their own But that's gone now.

"Kids now have more freedom to go to other places and they watch more telly; there are more outside influences and they have changed how they speak. They are doing away with flat vowels and using longer sounds."

Dr Clive Upton, a senior lecturer at Leeds University's School of English, said: "It's as though the younger generation is poshing-up the old dialects.

"Local people will always be the real experts and be able to tell who's from Bradford and who's not, but it's getting more and more difficult for people from outside to tell.

"Language has never stood still. People say we don't speak like our grandparents but those grandparents didn't speak like their grandparents either."

Mr Robinson said the site at www.collectbritain.co.uk, which has been funded by the National Lottery's New Opportunities Fund, was a treasure trove of local and social history.

The collection of voices pulls together two large archives from a survey of English dialects recorded by Leeds University in the 1950s and then the Millennium Memory Bank recorded by the BBC in 1998/9.

The two Bradford voices on the site belong to a pensioner who worked in Lister's Mill as a girl and a farmer who remembers when Wibsey Horse Fair was the biggest horse market in the country.