Have you been getting your history from Mel Gibson films or something? Britain did not pursue the war against the colonists with anything like as much ruthlessness as it could have done, especially by the standards of the day. They weren't even as ruthless as they might have been with foreigners, as the colonists were viewed as fellow Englishmen at that time, and many of the officers, even the ones who didn't refuse to fight against them, were, like Cornwallis, sympathetic towards the colonists' grievances....
Their real worry was the ripe situation for the Royal Indian Army, Royal Indian Air Force and the Royal Indian Navy (together, the largest all-volunteer force in WW2) toward turning against them. Hundreds of defections to militant nationalistic movements brought them more sleepless nights than any speech Gandhi might have made.
They feared turn-coats from this:
more than they feared this:
or this: