DETECTIVES are appealing for information about an incident involving the hijacking of a Royal Mail lorry, loaded with private mail, on Thursday, June 8.

At 8.50pm, a man sneaked into the Ascot Road sorting office in Watford, dressed as a postman and asked a member of staff if he could hitch a lift home in his lorry.

But when they were a short distance from the office he said he felt sick and the driver pulled over.

The bogus postman then threatened him with a substance similar to CS gas. There was a struggle before a second man jumped into the lorry and the driver was bundled out of the cab.

The robbers sped off in the DAF 600 bright red lorry, registration number S32SLC with the Royal Mail emblem on it, taking thousands of private letters and items of recorded mail with them.

A Post Office spokesman said it was not clear how the man managed to get into the sorting office.

He added: 'We know that about half of the load was priority recorded items which can be traced easily, but the rest of the mail will be harder to find.'

The bogus postman was about 5ft 8ins tall, aged in his early 50's with a ginger beard and a ruddy complexion, wearing black rimmed glasses.

His accomplice, was of medium build, in his 30's and believed to have been wearing a green bomber jacket and a luminous yellow top.

Detective Sergeant John Arthur, of Hertfordshire Constabulary CID, said his team was trying to establish exactly what the robbers were after. He hoped a detailed list of the lorry's contents, due to be provided by the Post Office, would shed some light on the incident.

He said: 'We don't know what we are dealing with at the moment. It was obviously well planned.

'We are appealing for anyone who saw the second man who was hanging around the Ascot Road link road to the depot and the Whippendell Road roundabout. We are anxious for information which will help us recover the lorry.'

Anyone with information can call Mr Arthur on 01923 472065/7.

Police are not linking the robbery to a similar incident in Rickmansworth, see page 11.

A 40-year-old man from Watford has been arrested in connection with the robbery, but has not been charged and was bailed until July 11 pending further inquiries.