Part of the problem is that Indian elites HATE being reminded how dirt-poor the vast majority of their populace really is. There are more poor in India than in the 26 poorest countries in Africa. And it's a kind of poverty that takes your breath away. In one part of northern India, people survive on a diet of river rats.
Indian politicians also hate the way that DFID has been able, with some degree of success, to target the aid where it's needed, and keep it out of the greedy, corrupt clutches of those same Indian politicians.
Of course the Indian politicians should pay for this - they're clearly more than rich enough, given the horrendous levels of corruption they shamelessly indulge in. But they won't. There's more money to made from skimming a cut from deals like the one they've just made with the French.
The Tories are being naive, quite frankly, if they think that aid oils the wheels with such craven elites as those in India. You either do this kind of thing because you think it's right, or not at all.