Mother-of-two Gillian Merrick, 45, had enjoyed a quiet family celebration with husband, Nick, and their teenage son and daughter before she disappeared in the middle of the night.

Mrs Merrick, who is recovering from a back operation and has difficulty walking, was last seen on the outskirts of Oundle, where she lives, in the early hours of Friday.

Police intensified a search over the weekend, drafting in the force helicopter and sniffer dogs, conducting door-to-door enquiries and searching nearby parkland and countryside.

Dozens of friends and neighbours joined in, but with overnight temperatures dropping below freezing, officers say they are becoming "increasingly concerned" for her safety.

On Sunday, her husband told of the family's anguish.

Mr Merrick who works as an engineer at Black and Veatch, which is a contractor for Anglian Water, at Thorpe Wood, Peterborough, where his wife is also employed as an administrator, said: "We are all getting extremely worried and the children are missing her desperately.

"We have had so many hugs and cuddles in the last couple of days and all we want is to have Gill back with us.

"The last thing she said to me on Thursday night was that she loved me. I told her I loved her, too, and that was the last time we saw each other."

Mrs Merrick had spent New Year's Eve at home with her husband and their children, Tom, 15, and Charlotte, 14, both pupils at Prince William School in Oundle.

The family went for a walk and a pub lunch on New Year's Day in nearby Wadenhoe, before returning to their home in Sutton Road and settling down to watch television.

The couple then went to bed, but when her husband woke up in the morning, Mrs Merrick was gone.

Mr Merrick said: "Gill loved walking and went out twice a day around the town on what we called her 'getting better walks' after her back operation about six weeks ago.

"But she was very safety-conscious and would never go out if it was frosty or drizzly, in case she slipped.

"She can't abide the cold, so to go out at whatever time it was in the morning not dressed for the weather and without walking shoes on, that alone is completely out of character.

"She adores the children. They are smashing kids and you couldn't ask for better.

"She gets on well with everyone and we had already made lots of plans for the year ahead. I just can't understand it."

Police believe Mrs Merrick may have been seen walking south along the A605, about a quarter of a mile from the Oundle roundabout, between 2am and 3am on Friday.

She is slim, about 5ft 6ins tall, with collar-length brown hair and is thought to have been wearing a beige jacket, red scarf and gloves.

A police helicopter has been searching the surrounding area and specially-trained search dogs from Dyfed-Powys police in Wales arrived last night to help.

Mr Merrick, his children, and about 40 relatives, friends and neighbours joined officers as the scale of the search increased yesterday.

Detective Chief Inspector Andy Cox said the hunt was focusing on areas including Barnwell Country Park, the River Nene near Ashton Mill and countryside alongside the A605.

He urged people living nearby to check garden sheds and outhouses in case Mrs Merrick had sought shelter.

Anyone with information should call Northamptonshire police on 08453 700700.