The number of Metropolitan Police staff in Britain investigating the disappearance of Madeleine McCann is being dramatically reduced, from 29 to four.

The girl was three-years-old when she vanished while on a family holiday in Portugal in May 2007.

Her parents Gerry and Kate McCann were dining with friends nearby their rented holiday apartment in Praia da Luz when Madeleine went missing.

Portuguese police abandoned their investigation after 15 months without establishing any clues to the mystery and for three years there was no official search for Madeleine.

Scotland Yard, with support from the British Home Office, began a review of evidence in 2011 and then launched a full-scale investigation two years ago.

The probe has cost millions of pounds, but so far no arrests have been made.

Assistant Commissioner of the Metropolitan Police Mark Rowley said, "this work has enabled us to better understand events in Praia da Luz the night Madeleine McCann went missing and ensure every possible measure is being taken to find out what happened to her.

"We still have very definite lines to pursue which is why we are keeping a dedicated team of officers working on the case. We have given this assurance to Madeleine's parents, Kate and Gerry McCann," he added.

Kate and Gerry McCann thanked all the staff involved in the investigation "for the meticulous and painstaking work that they have carried out over the last four and a half years. The scale and difficulty of their task has never been in doubt.

"Whilst we do not know what happened to Madeleine, we remain hopeful that she may still be found given the ongoing lines of enquiry".