The point is, there's no way legally in which they could reintroduce the Death Penalty in the UK.

Not unless somehow they could get every other country in the European Union to agree to bringing it back - and one problem with that would be, in a referendum on this in Ireland a couple of years ago people voted to amend the Irish Constitution to make it impossible to restore the Death Penalty, without another Constitutional Amendment which would require that people voted the other way.

Or theoretically the UK could pull out of the European Union completely. Which won't happen.