Deported offenders will be barred from re-entering UK and measures will apply to those in custody too to cut costs

Most foreign criminals convicted by a UK court will be deported immediately, instead of 30% of the way through their prison sentences, under plans announced by the government.

The justice secretary, Shabana Mahmood, has proposed a change in legislation that will give the government the power to deport most foreign prisoners as soon as they are convicted and incarcerated.

However, foreign terrorists, murderers and other serious offenders who have been given indeterminate sentences will continue to serve their time in the UK before being considered for deportation.

Prison governors will also retain the power to decide against deporting a foreign criminal who has been given a fixed-term sentence – known as a determinate sentence – if, for example, they consider the offender poses such a serious threat to the UK’s interests or national security that they should remain behind bars in a British prison.