Missing: The book will raise money to fund the search for Madeleine McCann

Madeleine McCann’s parents have signed a multi-million pound book deal to write about their daughter’s disappearance.

Kate and Gerry McCann’s emotional account about their four-year-old vanishing from a holiday apartment is an attempt to raise money to continue the search for her.

Profits from the book – which is expected to be one of next year’s best-sellers – will be donated to the family’s official fund to find Madeleine.

The book, simply entitled Madeleine, will be published on April 28 next year to coincide with the fourth anniversary of their daughter’s disappearance.

It comes as earlier this month they revealed that the dwindling fund would run out of money by early 2012.

Within weeks of Maddie being snatched from a holiday apartment in Praia da Luz, Portugal, in May 2007 money from the public poured in to boost the Find Madeleine Fund. At its height it stood at £2 million. But now there is just £300,000 left.

Precise details of the publishing deal have not been released, but a source said it included a ‘substantial’ advance and included ‘enhanced royalties’ - giving the couple a bigger share of profits from sales.

Mrs McCann, 42, said: ‘My reason for writing is simple - to give an account of the truth. ‘Publishing this book has been a very difficult decision and is one that we have taken after much deliberation and with a very heavy heart.

‘However, in the last few months, with the depletion of Madeleine’s Fund, it is a decision that has virtually been taken out of our hands.

‘Every penny we raise through its sales will be spent on our search for Madeleine. Nothing is more important to us than finding our little girl.’

Mr McCann, also 42, added: ‘We are hopeful that this book may help the investigation to find Madeleine in other ways too.

‘Our hope is that it may prompt those who have relevant information - knowingly or not - to come forward and share it with our team. Somebody holds that key piece of the jigsaw.’

Transworld won the rights to publish the book - which is being written by the McCanns themselves and is currently part-complete - in the UK, the Commonwealth and Europe.

It is expected to sell thousands of copies due to the overwhelming interest since her disappearance in April 2007 and be priced at £20.

The publisher is home to best-selling authors including The Da Vinci Code writer Dan Brown, fantasy novelist Terry Pratchett and theoretical physicist Stephen Hawking.

Transworld publisher Bill Scott-Kerr said: ‘It is an enormous privilege to be publishing this book.

 ‘We are so pleased to be joining Kate and Gerry McCann in the Find Madeleine campaign.’

Deals for newspaper serialisations and translations of the book are now expected to be negotiated.

The McCanns, from Rothley, Leicestershire, are fighting a legal battle against former Portuguese detective Goncalo Amaral over his book alleging that Madeleine died in the apartment and that her parents faked her abduction - something they strongly deny.

The appeal court in Lisbon last month overturned an injunction obtained by the couple banning publication of Mr Amaral’s work, Maddie: The Truth Of The Lie.

But a source close to the McCanns said their decision to write their own book had nothing to do with rebutting Mr Amaral’s allegations.

‘It certainly hasn’t been prompted by him,’ the source said.

Earlier this month, Mrs McCann admitted she ‘had to face up to the fact’ that her missing daughter may never be found.

Mrs McCann also accused the Government of giving up the hunt for the child, who went missing shortly before her fourth birthday.

She said a series of ministers had shrugged off her pleas for help. ‘I don’t want to be appeased, and that’s what I feel we’re getting. We need action, I don’t need fluffy worthless words,’ she said.

The couple have written an open letter begging for political and financial help and launched an online petition to lobby the British and Portuguese governments for a formal review of the case.

Portuguese police shelved an 18-month investigation into the disappearance after clearing her parents as formal suspects, and the case has remained closed.

Madeleine was four when she vanished from her family’s holiday apartment in Praia da Luz in the Algarve on May 3, 2007, as her parents dined with friends nearby.