Carlos Sheen, of Lillington, works as a part-time street cleaner for the Sita recycling and waste management company, based at the Blick Road depot in Warwick.

He was made aware that an "offensive" poster of himself was put on display at the depot's office in May this year.

Shortly after the incident, Mr Sheen said one of the employees at Sita admitted to him that they were responsible for putting up the poster.

After putting forward a grievance to the company, a hearing was held in August and adjourned. But Mr Sheen received a letter on September 16 informing him that the case had been closed and no further action would be taken.

He said: "I feel that the company has not done enough - the person responsible should be disciplined.

"Even if they cannot pin them down, the person who told me about the picture waited a whole day to take it down. Surely they have a responsibility to have respectfully removed it immediately.

"To me, it has not been dealt with adequately. I am striving for more action to be taken. Sita should have done its utmost to find the culprit.

"Something has gone amiss. I feel uncomfortable working for a company where you are being singled out."

Mr Sheen said he knew of a similar incident last year at the company - then known as Verdant - when an Afro-Caribbean employee at the Warwick office was depicted in an offensive poster.

Mr Sheen, who also has a full-time job as a stores controller in Warwick, approached the Race Equality Partnership, in Hamilton Terrace.

He added: "The partnership was happy with the summing up after the investigation because Sita said it would be organising diversity training for all employees."

"I don't even believe that training has taken place."

Sita's human resources and communications director, Kevan Sproul, said: "After we received the complaint from Mr Sheen we carried out a thorough investigation, which lasted for several weeks.

"The reason it was adjourned on a number of occasions was down to the thorough nature of the investigation and the fact that, in discussion with Mr Sheen, we followed up all potential lines of enquiry.

"We were unable to discipline any members of staff because the investigation did not identify which individual was responsible.

"Therefore the most appropriate course of action was for us to provide a diversity awareness course to all members of staff, which has now taken place.

"Mr Sheen is a valued employee and the welfare of our staff is paramount to us."

The Courier approached the Warwickshire Race Equality Partnership but a spokeswoman for the organisation said she was unable to comment on individual cases.