Detectives investigating the theft of a pensioner's body from a grave were given a further 36 hours last night to question four people arrested as part of the inquiry.

The three men and one woman were detained on Tuesday on suspicion of conspiracy to blackmail. Detectives had until 9pm last night to decide on their next course of action.

A Staffordshire Police spokesman last night said they had been granted a 36-hour extension by magistrates to continue questioning the four.

They were arrested nearly 12 months after 82-year-old Gladys Hammond's remains were stolen from a graveyard in Yoxall.

The theft has been blamed on animal rights extremists opposed to Mrs Hammond's family's involvement in a farm that breeds guinea pigs for medical research.

Those being questioned on suspicion of conspiracy to blackmail David Hall and partners, who run Darley Oaks farm, at Newchurch, near Burton-upon-Trent, are three men aged 35, 36 and 38, and a woman aged 37.

The men were arrested at addresses in Manchester, the Edgbaston area of Birmingham and Wolverhampton. The woman was detained in Burntwood.

A 23-year-old woman who was also arrested at the Wolverhampton address on suspicion of obstructing police and assaulting an officer was released on police bail on Tuesday night.

Those in custody have all been arrested previously as part of the inquiry.