Police are investigating a series of poison pen letters written by a "lone nutter" and concerning a Watford councillor.

Six letters have been sent since August making "unfounded and malicious" allegations against Mark Watkin, Liberal Democrat councillor for Nascot ward.

The recipients of the letters are reported to be Liberal Democrat supporters, though delivery of the typed documents has not been confined to the boundary of leafy Nascot ward.

The case is considered so serious Hertfordshire Constabulary's Major Crime task Force is investigating the matter.

Councillor Watkin, 59, from Melrose Place, was elected to Watford Borough Council in May last year and has three more years in office before facing re-election.

Since August 28, 2006, the letters have been sent to addresses in Melrose Place, Greenbank Road, Perivale Gardens and Swiss Avenue. The latest letter was received on Wednesday and it is believed they are the latest tool in a two-year campaign against him.

In a statement, father-of-three Councillor Watkin, who is married to Elizabeth, said: "I am completely bemused as to why anyone would do such a horrible thing, but I am delighted that the police are taking this very seriously.

"I hope they catch the perpetrator as soon as possible."

Watford Mayor Dorothy Thornhill said: "This is a hate campaign. Nobody wants a nutter in their ranks. This is a lone nutter who is not working on anybody's authorisation.

"Clearly this is somebody who is politically motivated but not party politically motivated. Any ordinary party person will be shocked by it. It is unprecedented."

For full story see this week's Watford Observer, on sale now.