Gillian (45) was last seen at 11pm on New Year's Day, after which it is believed she went out for a walk in Oundle, where she and her family live.

Throughout last week a major police search was carried out, with divers searching rivers in the area and officers with specialist search dogs and helicopters scouring the countryside for the mum of two.

While the police operation was scaled down over the weekend, husband Nick (49), children Tom (15) Charlotte (14) and dozens of friends and colleagues at Peterborough firm Black and Veatch, where Mr and Mrs Merrick worked, continued the hunt – concentrating on Ashton, a village near where they live.

Anyone with information is asked to call Northamptonshire police on 08453 700700.

Searches were carried out through country lanes and along the waterways in freezing conditions on Saturday and Sunday, and are set to continue throughout this week

More leaflets and posters appealing for more information were handed out and displayed throughout the village by the volunteers.

Two potential sightings of Mrs Merrick were reported during a police operation on Thursday last week, when more than 300 drivers were stopped and questioned on the A605.

Officers are continuing to sift through the responses, and are keen to follow up sightings of a woman walking away from Oundle along the A605 in the early hours of Friday, January 2.

Sussex Police had also been called in to help the investigation in the Forest Row area, where the family used to live.

At the weekend Mr Merrick released family photographs featuring Mrs Merrick to try and jog the memory of anyone who may have seen her in the past week.

He also spoke of his gratitude to the dozens of people who had helped in the search, and his hope that she would be home soon.

He said: "It sounds trivial but we want to say thank you. I don't think people realise how much their help means. So many people have gone out in the cold to help us."

Mrs Merrick is 5ft 6ins tall with straight brown collar-length hair.

She is thought to have been wearing a beige jacket, red scarf and red gloves.

Anyone with information is asked to call Northamptonshire police on 08453 700700.