More than 600 children, the majority under 12 years old, have been put in detention under immigration rules in the four years since the Government claimed to have ended the controversial practice.

A new analysis of Home Office statistics by The Independent also reveals that the number of children being held increased from 127 in 2011 to 228 in 2013 – an 80 percent rise. This is despite Deputy Prime Minister Nick Clegg stating in December 2010: “We are ending the shameful practice that last year alone saw over 1,000 children – 1,000 innocent children – imprisoned.”

At the time he promised child detention would be stopped except as an “absolutely last resort, involving what we predict will be a tiny number of cases... immediately prior to [the children] leaving the country.”

But since he made that pledge, official figures indicate that 661 under-18s – most of them from families seeking asylum – have been detained.

Around half end up being allowed to stay in Britain rather than being deported. In some cases children have remained in detention for weeks before being released.

Simon Parker, of the End Child Detention Now campaign group, said: “Although the numbers of children being detained are considerably lower than under the previous government, what Nick Clegg called ‘state-sponsored cruelty’ is still happening to hundreds of vulnerable children. It is time that we ended this unnecessary and harmful practice once and for all.”