Police say they have not recovered Mrs Hammond's remains

The remains of Gladys Hammond, whose son-in-law helps run a farm breeding guinea pigs for medical research, were dug up in Yoxall, near Lichfield.

Animal rights activist John Curtin, 41, of Coventry, was thought to have been one of those held over the theft.

The other man was a 34-year-old from Wolverhampton, police said.

Mrs Hammond's body was removed from her burial plot at St Peter's Church under cover of darkness last week - police have still not recovered her remains.

It is thought that at least two people were involved in digging up the grave of Mrs Hammond, whose family have repeatedly been targeted by animal rights extremists.

Police called in the coroner after the grave was desecrated

Staffordshire Police said a 41-year-old man in Coventry and a 34-year-old man in Wolverhampton were arrested on Thursday morning.

Animal Alliance member Nancy Phipps, whose daughter Jill was crushed to death under a lorry during a protest at Coventry Airport in 1995, said Mr Curtin had been arrested at his home in Adelaide Street.

Mrs Phipps said: "John's door was knocked down this morning despite the fact he has had nothing to do with the Newchurch protest. The police are just on a fishing trip.

"John is well known in the movement and he's a campaigner and a good speaker. He has converted to Buddhism and he's a gentle person."

Mrs Hammond, who died in 1997, was the mother-in-law of Chris Hall, one of two brothers who run Darley Oaks Farm in Newchurch, Staffordshire.