Madeleine McCann's mother Kate has arrived at a police station in Portugal to be re-interviewed by detectives investigating the four-year-old's disappearance.

Mrs McCann was driven to Portimao by her husband Gerry from their rented house in Praia da Luz.

He dropped her off at the entrance and gave her a goodbye kiss.

Mr McCann will be questioned separately tomorrow.

Sky News Crime Correspondent Martin Brunt said police wanted to re-interview the McCanns as witnesses.

But he added: "According to the McCann family it appears to be more formal."

Portuguese police called Mr McCann on Monday to request the interviews, specifying that Mrs McCann should be questioned first.

It is only the second time she has been formally interviewed by police, the first being on May 4, the day after Madeleine went missing.

Detectives have already questioned Gerry McCann twice.

It is expected that Mrs McCann's interview will be longer than the one she gave officers in May, which lasted between three and four hours.

The development comes after officers leading the investigation were given DNA test results.

Sky News has learned vital clues from the results are expected to lead to a significant development.

Experts at the Forensic Science Service (FSS) in Birmingham have spent the past month analysing samples taken from the McCanns' holiday apartment in the Algarve resort of Praia da Luz.

The evidence recovered includes blood flecks found by British sniffer dogs on the wall in Madeleine's bedroom, where she vanished on May 3.

A source has confirmed that information gathered by the FSS had been "regularly fed back" to investigators in Portugal, although the official line remains that tests are "ongoing".

An FSS spokeswoman would not comment on the specifics of the case, but said: "There has been a lot of speculation. The tests are ongoing.

"There has been no change in that, despite what the reports say. It's a live investigation and we are working with the police."

The only official suspect in the case, 33-year-old ex-pat Robert Murat, believes the Portuguese authorities will shortly clear him formally.

His spokesman Tuck Price said he had not been told about any developments in the case.

"Why are they holding him in limbo?" he added. "That is still a concern - unless they are using him as cover so that they can continue investigating somebody else...

"It's still very frustrating - it's been five weeks since they went back in there again (to search Mr Murat's house for a second time), and we thought this would all be sewn up."