The incidents involved people pretending to be from the council, social services, the water company or police.

On Thursday morning, a woman claiming to be from the council lured an 80-year-old man into the garden of his Irchester home while an accomplice stole cash from his house.

A similar incident took place that afternoon in Higham Ferrers.

The woman involved in both incidents is described at white, between 20 and 20 years old and 5 ft 4 ins, with brown hair. She was wearing a brown coat and possibly a brown hat.

Teams suspected

A man seen nearby has been described as white, aged about 30 to 40, about 5 ft 6 in tall and wearing a black woollen hat.

Two men also called at a house in Bayes Street, Kettering with a story about having been sent to turn the water off.

It was the first of two similar incidents in Kettering on that day.

And a caller in Southlands entered a house on Thursday evening with a claim that he was from "the water board" and stole money from an elderly man.

Police believe that the offences in the eastern area of the county are linked, as are the offences in the northern area - and they are currently looking at the possibility that all five offences were carried out by the same team of people.

Officers appealed for people to call in with sightings of anyone behaving suspiciously by lurking in neighbourhoods, knocking on several doors in a street or sitting in vehicles.