Ministers have been warned by an official immigration watchdog of the "excessively long" periods, including cases of more than three years, that detainees are being held at Europe's largest removal centre.  A "snapshot" taken last December showed that 35 detainees at Harmondsworth removal centre, near Heathrow airport, had been waiting more than 12 months to be deported, including seven who had been waiting more than two years. Harmondsworth's officially appointed independent monitoring board (IMB) said one man had been held in detention for three years and seven months at a cost of £110 a night. The bill is already more than £144,000.