www.bbc.co.uk/news/uk-29019431
I don't see how its possible to remove British nationality from someone who was born in the UK. It would leave them stateless. The European Human Rights Act makes it impossible to hang someone in the UK for high treason. (As tempting as it might be to hang the person who beheaded that poor journalist in syria.)
Surely the answer is for Jihadists to be tried and punished in the accordance with the laws of the countries that they have have committed attrocities. However to put it politely the burden of proof is not quite so strict as the UK in many Islamic states. We also have laws about sending British citizens to places where they might be on the recieving end of torture or the death penality.