Image copyright PA Image caption Madeleine McCann was three when she went missing in 2007

Police are following one remaining line of inquiry into the disappearance of Madeleine McCann, Scotland Yard boss Sir Bernard Hogan-Howe has said.

The UK-based investigation into her disappearance could finish in the next few months, he told LBC radio.

Madeleine, of Rothley, Leicestershire, was three years old went she missing from her family's Portuguese holiday apartment on 3 May 2007.

Despite a high-profile hunt, no trace of her has ever been found.

The remaining line of inquiry is centred around a letter asking for assistance sent from UK investigators to the Portuguese Public Prosecution Service in July 2015.

In October last year, the Metropolitan Police confirmed that the number of UK officers investigating the case had now dropped from 29 to four, as the majority of work on the case had been completed.

Madeleine's parents, Kate and Gerry McCann, said then that they fully understood the decision.

Thursday 3 May 2007: Timeline

20:30 Kate and Gerry McCann leave their apartment to have dinner at a Tapas bar

Kate and Gerry McCann leave their apartment to have dinner at a Tapas bar 21:05 Gerry McCann checks on Madeleine and her siblings

Gerry McCann checks on Madeleine and her siblings 22:00 A man is seen carrying a child wearing pyjamas heading towards the ocean

A man is seen carrying a child wearing pyjamas heading towards the ocean 22:00 Kate McCann raises the alarm that Madeleine has gone missing

Clickable map and timeline

Sir Bernard said: "There's been a lot of investigation time spent on this terrible case.

"It's a child who went missing, everybody wants to know if she is alive and if she is where is she, and sadly if she's dead then we need to give some comfort to the family.

"It's needed us to carry out an investigation together with the Portuguese and other countries have been involved.

"There is a line of inquiry that remains to be concluded and it's expected that in the coming months that will happen."

He said that line of inquiry was agreed to be "worthwhile pursuing" but once that had concluded, the probe, called Operation Grange, would likely end.

But he added: "If somebody comes forward and gives us good evidence we will follow it. We always say that a missing child inquiry is never closed."

Met investigation 1,338 statements taken 1,027 exhibits collected 60 persons of interest investigated

8,685 potential sightings considered

560 lines of inquiry identified

30 requests made to other countries asking for work to be carried out

The Home Office requested a review of the case in May 2011. Operation Grange, which has been supporting the Portuguese police's investigation, became a full investigation in July 2012.

The Met said in October that officers had finished bringing together and investigating the information held by Portuguese police, the UK investigation and private investigators working on behalf of the McCann family.

The inquiry took 1,338 statements and collected 1,027 exhibits but has not yet reached a conclusion.

Officers investigated more than 60 persons of interest. A total of 650 sex offenders were considered as well as reports of 8,685 potential sightings of Madeleine around the world.

Having reviewed all of the documents, "7,154 actions were raised and 560 lines of inquiry identified", the Met said.

More than 30 requests were made to "countries across the world asking for work to be undertaken on behalf of the Met".