Britain's largest parking company is investigating an anonymous letter condemning working conditions for Brighton's traffic wardens.

The letter is said to come from a group of wardens working for NCP, which is contracted to Brighton and Hove City Council to provide traffic management.

It says basic errors made by stressed staff mean thousands of parking tickets could be invalid. There are also allegations of sexism, drug-taking, racism and homophobia among the ranks. It is claimed abusive language is rife and disabled drivers are dismissed as "gimps".

The claims are being treated with caution by the council and the NCP but both are investigating. NCP has a policy of allowing staff to raise concerns without fear of intimidation, but the self-styled "whistleblowers" have refused to reveal their identities. Nor does the letter give evidence in support of the claims.

NCP spokeswoman Jackie Nixon said: "We will be investigating all the issues raised, will discuss these with our employees and take appropriate action."

A parking attendant from Brighton told The Argus: "Levels of stress-related sickness and resignations have now reached an all-time high at Brighton."

The letter complains of poor facilities in the Brighton office, including male and female wardens having to share a changing room. The letter is addressed to the Health and Safety Executive (HSE) but managers at the HSE say they have not received it.