FANS are set to scramble for tickets after it was announced Coldplay and Lily Allen will perform in a once-in-a-lifetime concert in Exeter city centre.

The stars are coming out for a Mencap Big Noise charity concert being held at Exeter Castle.

They will be appearing with electric-pop duo La Roux before a crowd of just 500 in a marquee on Saturday, December 19.

The event is the idea of DJ and Mencap supporter Jo Whiley.

Coldplay’s lead singer, Exeter-born Chris Martin, said: “I don’t think there could be a better way to end the decade... La Roux, Lily Allen, Jo Whiley — what more can you ask for?

“It is going to be really, really special.”

The night will mark a festive homecoming for Chris — who last played Exeter nine years ago — and a spectacular treat for the 500 lucky fans, with all proceeds going to learning disability charity Mencap.

Tickets, at £50 a time, will be available from Tuesday, December 8, with a limited number going on sale at HMV, in Princesshay, Exeter, on Thursday, December 10.

La Roux, Lily Allen and Coldplay will be performing “unique, stripped back sets”, promising a rare treat for the audience.

Exeter’s bumper Christmas present comes hot on the heels of last month’s hugely successful Mencap Little Noise Sessions which, over 10 nights, saw artists including the Arctic Monkeys, Lostprophets and David Gray perform acoustic sets at Islington’s Union Chapel.

Now in their fourth year, the Little Noise Sessions are hosted by Radio One DJ and Mencap ambassador Jo Whiley.

She, along with Coldplay’s Chris, has been the driving force behind this new event, Mencap’s Big Noise Session.

Jo said: “This gig has all the right ingredients — a beautiful location, Christmas spirit, one of the best bands in the world and special friends all in an intimate setting. Add mulled wine, mistletoe, candles and carols and this will be the ultimate winter warmer.

“I couldn’t be more thrilled that Coldplay, Lily and La Roux want to make a big festive noise for Mencap.”

Chris added: “We’re proud to support Mencap and, for me, it’s exciting to play my hometown. We haven’t played there since 2000.”

Coldplay formed in 1998, and in less than a decade have become one of the world’s biggest bands with over 40 million record sales and an army of fans across the globe. Fronted by Chris, the band have notched up a raft of hits including Yellow, Clocks, The Scientist, Fix You, Speed Of Sound, Violet Hill and Viva La Vida.

Lily Allen, 23, has been described as Britain’s most consistently engaging pop star, as well as one of the most successful. This month Q Magazine named the singer one of the Artists Of The Century, highlighting those who have made an impact on the music industry over the last decade.

Electropop band La Roux is made of up of singer Elly Jackson and synth player, co-writer and co-producer Ben Langmaid. Influenced by 1980s synthpop, the duo burst on to the scene its year enjoying massive success with hits including In For The Kill, Bulletproof and Quicksand taken from its self-titled debut album.

Guy Wadsworth, of the Exeter Castle Partnership which runs the castle, said: “This is a great coup for us and the city and we are really pleased to have such big names appearing here.

“It has been in the planning for some months and we have been in consultation with the police and fire services. It’s all clear.

“We do quite a lot for charity, with the Royal British Legion having free use of an office here, and we are delighted to be able to do our bit for Mencap.

“We are giving the site free of charge for the event which should be one of the biggest and best concerts in Exeter.”

Those hoping to hear the concert from outside the castle — which adjoins Northernhay Gardens — may be out of luck.

Mr Wadsworth said: “It is unlikely they will hear much if anything because it will be in a marquee behind the castle walls — and I understand it will be quite a pared-down, acoustic performance.”

The Echo’s Teen teamers also welcomed the news.

Becca Stokes, 16: “It’s brilliant that they’re coming here. Nobody famous ever comes to Exeter, they usually stop at Bristol, so this is great news.”

Beth South, also 16, added: “I’m glad that we’ve finally got some performers who are more popular coming to Exeter, instead of the usual dance and trance staff.”

Lauren Tremlett, 16, said: “Coldplay and Lily Allen are very popular; it’s a shame there’s only 500 tickets — a lot of fans are going to be left disappointed.”

Ambitious plans at Exeter Castle to turn the former courts complex into the Covent Garden of the South West are currently on hold because of the recession, but parts of the listed building are being used as offices, art space and residential accommodation.