White male recruits to the Metropolitan Police are having to wait up to three years to join as ethnic minority and women applicants are being prioritised.
Ethnic minorities currently account for about 17% of all new recruits
The recruits are among 10,500 - taken on by the UK's largest force between 2001 and 2003 - who are being sent for training in staggered intakes.
But the Met has tried to make each intake balanced, moving some women and ethnic minority recruits up the queue.
A spokesman said a more diverse force would deal with the community better.
The Met's human resources director Martin Tiplady said: "There is the potential that some white males will have waited up to three years to get in."
The force insists the move does not amount to positive discrimination because all of the successful applicants have been offered jobs.
A spokeswoman said: "The Met is always looking to improve the service we provide to the people of London.
"By balancing our intakes of recruits we can better prepare all of them for the job they will be doing."
However, Des Keenoy, the Metropolitan Police Federation's constables' chairman, said: "There is positive action which is legitimate, and positive discrimination which is not. The line between the two is getting very narrow indeed."
The Met is also close to introducing new criteria to prioritise applicants, including whether they speak a second language and whether they have "knowledge or experience of a community group".
Being a Londoner and a university graduate are also factors that would work in their favour.
Mr Keenoy added: "The criteria for joining should be the same for all - can you do a very complicated and difficult job as well as the next person?
"We need diversity, we need an eclectic mix of skills and knowledge, but by focusing on certain elements it may be to the detriment of the service overall. It is a debate that needs to be had."
Government targets stipulate that 25% of Met Officers must be non-white by 2009.
The proportion is currently around 7%, although ethnic minorities account for about 17% of all new recruits.
Commissioner Sir Ian Blair said recently that his force had little chance of meeting the target, which was one of the key recommendations from the inquiry into the Stephen Lawrence murder.