They were british citizens, I agree. Happy now?
But lets face it, those "british citizens of Pakistani origin" attacked India because of an identification they had with Pakistan not with the UK.
If they are of Pakistani origin, attack India because of an identification with Pakistan, and were trained in Pakistan to kill Indians, then its clear India is going to be looking to Pakistan to blame rather than the UK.
If a bunch of Mr Smiths from Surrey decide to get together with the local Cricket club, construct a training camp for armed warfare that the government decides to turn a blind eye to, and then they successfully lauch terror attacks on India. At that point the UK is going to be legitimately worried about India taking umbrage.
Until then, if some Pakistani's turn up here, don't integrate, construct unhealthy communities cut off from the rest of the UK, and then some of them produced from this terrible environment decide to sod off half way round the world to destroy the enemy of the country they first came from; then with all the will in the world the UK is in no position to stop it from happening. Why we can't is a whole new thread.