Criminals suspected of being in the UK illegally are not being properly dealt with by immigration officials, the Police Federation said.
Chairman Jan Berry told the BBC officers were "frustrated" and felt like they were "re-injecting" illegal immigrants back into society to commit further crimes.
"It's terribly frustrating for police officers where they have a person who they believe is in the country unlawfully," Ms Berry told the broadcaster.
"It's like a double whammy that not only do you not expect them to go into the system, you're also re-injecting them back into society where they can carry on committing crime."
She said officers felt let down by the Border and Immigration Agency's (BIA) failure to carry out proper investigations.
She said the agency told officers to let people go and instruct them to make their own way to immigration centres.
A BIA spokesman told the BBC that it was committed to the removal of foreign national criminals and that last year more were removed than ever before.
