Kate McCann has revealed she had thoughts about being "wiped out" in a motorway crash to end the pain of losing Madeleine.

Mrs McCann spoke of her dark thoughts ahead of the third anniversary of Madeleine's disappearance - but vowed never to give up her search.

She said: "I used to have thoughts like we'll get wiped out in the car on the motorway. So it would just happen, we'd all be gone, and the pain would be away...

"But what I do know now for sure is that I don't want that," she told the BBC World Service.

In an emotional address to her daughter Mrs McCann, 42, said: "We will never give up until we've found you.

"We love you very much, Madeleine, and we're not going to stop what we're doing."

Her husband Gerry, 41, added: "Madeleine, we're still looking for you. Tell someone who your mummy and daddy are, who you are."

Madeleine was nearly four when she went missing from her family's holiday apartment in Praia da Luz in Portugal on May 3, 2007, while her parents dined with friends nearby.

The couple still remain determined to find her but now feel less guilty about coping and enjoying themselves without her.

Mrs McCann said: "I'm able to look at it now and think actually it's positive we're functioning. It's positive for Madeleine and for (her siblings, five-year-old twins) Sean and Amelie."

Mr McCann compared their experience to that of fighting cancer and said: "There are different types of loss and I suppose losing a child is one of the hardest things to cope with."

"Fighting cancer over a long period is another similar battle - the difference with what we face compared to losing a child who's died is that we have an ongoing situation - and the unknown."

But, he said, laughter and happiness were essential for living a normal life.

"The guilt, where you feel 'Madeleine is missing so how can you enjoy yourself?' - that is much, much, much less than it was and I think if you're going to have some sort of normality, you've got to have some laughter and some joy."

Missing: Madeleine McCann

Both have admitted their ongoing ordeal has tested their Catholic faith however.

Mr McCann said: "When you think of the amount of prayers that a single child has received, you think if those prayers were going to work, they should have worked before now.

"The difficulty is you don't always get your rewards on this earth."

Despite a massive police investigation and huge publicity worldwide failing to lead to Madeleine's discovery, Mrs McCann said she believed the chances of finding her have not diminished.

She said: "The hardest thing is you don't know how you're going to find her, what it's going to take."

The McCanns believe police activity should renewed in search of their daughter.

"The key test is 'has everything that could reasonably have been done, been done?' And the answer to that is no," Mr McCann said.

"There's no law enforcement that's been proactively doing anything for 18 months."

The McCanns are expected to mark the anniversary in private and as yet have no plans for how they will spend the day.