> [in England ...] For me, the horn is a warning sign - "get out of my way" or "watch out!" - only to be used in emergencies.
That is not the correct use in England, especially not 'get out of my way' (emergency services' vehicles aside) - and it needn't be an emergency (uh, again!).
It's only supposed to be used to alert other drivers to your (non-stationary) presence, when it appears they haven't seen you or may not be afforded the opportunity - on a winding country road for example, less than two cars wide, it's common to sound it before a blind corner so that if you get one back you can both negotiate a careful passing, or the other car can pull over for you if they have the chance.
Which is pretty similar to what you describe in India really, just quite a different bar for when you need to warn of your presence!