People like that should be sent back immediately (after serving their prison
sentence) to the place where they come from and should no longer be allowed to stay.

Sent back immediately, or sent back after 20 years of imprisonment (at the taxpayers expense, of course)?

I remember a few years ago, some 'illegal' had entered the UK on false papers. After a couple of weeks he decided he didn't like it and tried to leave. However, this time he was caught at the border, arrested for having a false passport, and then sent to prison (at the taxpayers expense).

He was trying to LEAVE.....FFS!