'I'm certain I saw Madeleine outside Belgian cafe'

The more she thinks about it, the more convinced this woman is that she let slip the chance to reunite Madeleine McCann with her family.

The 33-year-old, a child therapist, was alerted by the strange behaviour of a couple with a blonde girl in a pink dress at a cafe in Belgium.

She felt sure the Dutch man and English-speaking woman were not the girl's parents and also thought the sad-looking child with the 'big, strong' eyes bore a striking resemblance to the missing English girl.

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But she wasn't sure. So she hesitated and did not call the police until the trio had driven away in a black Volvo estate.

Yesterday, nine days after the sighting - described by police as 'highly credible' - the woman said: 'I feel very guilty that I did not do more. I wish I had just grabbed her when I had the chance.

'I was hesitating and hesitating. The day afterwards I just felt so sick I had to go to the doctor.'

Belgian police have taken DNA samples from the bottle of Fristi milkshake and straw used by the girl at the De Pauze cafe in Tongeren, near the Dutch border. The results are due on Wednesday.

Madeleine's parents have said it is too early to get their hopes up.

The woman, who has a seven-year-old daughter, was alone in the cafe when she noticed the child. 'The girl was often looking at me,' she said. 'Her eyes were very big and strong.'

She added: 'Sometimes she was laughing and playing and other times she was sitting with a very sad face. It's very strange for a child to be happy and playing one minute then suddenly be very sad for no apparent reason.'

She said: 'The parents' behaviour was even more strange. They kept trying to play with the girl but I felt they were not used to playing with children. It did not look natural.'

She managed to get the first three letters of the Volvo's registration, VUV. Police have traced and eliminated several cars from the inquiry.