The sister of a policeman killed when his high-powered motorcycle hit a roundabout has criticised a council for not making the road safer.

Pc David de Burgh-Thomas died after being thrown from his Honda Fireblade on July 17.

The 40-year-old officer, a member of Thames Valley Police's northern area intelligence support team, was taking part in an undercover operation, an inquest heard.

He was travelling at more than 70mph when he crashed in Marlborough Street, Milton Keynes.

His sister Esther said that her brother, who lived in Banbury, died because he was "supposed to guess a roundabout was there".

In a letter to Milton Keynes Council, she wrote: "There is no roundabout sign until the last minute (the first one was, and still is, obscured by foliage), no yellow lines or raised rumble strips across the road, no 'reduce speed now' signs.

"Even the speed limit remains at 70mph right up until the end. And the roundabout is hidden from view."

Miss de Burgh-Thomas said she had been lobbying the council to cut back the foliage masking the sign and make it clearer to drivers that they were approaching a roundabout.

The inquest at Milton Keynes heard that the road was still unsafe.

Sgt Nigel Whelan, of Thames Valley Police, said signs leading to the roundabout were inadequate and there had been a number of other accidents there.

Recording a verdict of accidental death, coroner Rodney Corner said that Pc de Burgh-Thomas was totally unaware of the roundabout.

He added: "We will never know what prompted him to travel at that speed but it was during a police operation.

"Sadly, it takes an accident of this sort, involving highly-trained police officers, to bring it home that something needs to be done urgently about this roundabout."

George de Burgh-Thomas, David's father, said: "I feel strongly that if anything can be done to stop this happening to other people, then our son will not have died in vain."

Pc de Burgh-Thomas leaves a widow, Yvonne.

No-one from Milton Keynes Council was available for comment about the coroner's remarks.