The appeal court judges upheld an award of£1,500 compensation to Raham Khan under the Race Relations Act.
The master of the rolls, Lord Woolf, said Mr Khan, then a sergeant in the West Yorkshire force, believed he had been discriminated against on racial grounds because of the chief constable's failure to support his application for promotion to inspector.
Mr Khan, now aged 43, made a complaint to an employment tribunal in 1996 and, in the meantime, applied for a new job with the Norfolk police.
'In the light of that, the chief constable is unable to comment any further for fear of prejudicing his own case before the tribunal.'
Lord Woolf said Mr Khan's application to the Norfolk force - although unsuccessful - had been given consideration and had not in fact been prejudiced by the terms of the chief constable's letter.
But he was not aware of that at the time and 'he could naturally be distressed to think that he might not obtain a job which he wanted because of the refusal of his employer to provide a reference'.
The employment tribunal in 1997 dismissed Mr Khan's allegations of direct racial discrimination, but upheld his victimisation claim.
Although he had suffered no financial loss, the tribunal awarded him£1,500 for 'injury to his feelings' said Lord Woolf.
The chief constable's appeal against the tribunal's ruling was later dimissed by the employment appeals tribunal.
Lord Woolf, sitting with Lady Justice Hale and Lord Mustill, agreed that Mr Khan had been 'treated less favourably' when it came to the job reference because he had lodged a complaint with the employment tribunal.
Dismissing the chief constable's appeal, the judge ruled: 'The decision of both tribunals was correct.'
Although the award of£1,500 'seemed high', the appeal court judges declined to reduce Mr Khan's pay-out.