They didn't have TIME to deal with them. From [1] The Sun, with thanks to Teri:

ANGRY cops had to free two dodgy asylum seekers because immigration staff were too BUSY.

The two illegals were detained at a police station after 11 YEARS on the run.

But immigration officers admitted they did not have TIME to come and get them — despite being only four miles away....

Algerian Abdul Alouane, 35, and Nigerian Mohammed Egbejule, 28, were stopped in a suspect car in South London.

They were taken to Brixton nick and cops called the immigration processing centre at London Bridge — only to be fobbed off.