'But he did serve time in Pakistan yes? if that is the case and the crime involves terrorism in the UK surely the Home Office would have the option to revoke his UK nationality assuming he has dual citizenship in Pakistan of course'
The law in Pakistan is somewhat more flexible in terms of the burden of proof required for guilt to be established than in a British court. Legally it is not possible to revoke the citizenship of someone British, born in Britain and of British parents. I strongly suspect that if the home office have not charged him, it is because they have insufficient proof, or they see more value in observing his next move.
OK got it thanks :-)