Hi all, thank you so much for all your replies and apologies for replying so late. They've all proven useful - I did contact one of the ladies in the link Ciderdrinker posted and unfortunately she didn't know the history of the Garlah name, but knew the ladies who ran a school in Mussoorie.
I was wondering if Garlah was an anglicized Indian name, but from what you've said, Ciderdrinker, it looks like it could be English. So a Garlah went to India at some point and settled there. Thank you for those English references to Garlah - they give me more of a possible idea. (I did manage to sit down and unpick the Charlesworth references on Familysearch, and managed to work out the three wives of William(!) and their children, so I now have a clear line from my g grandfather William Jonathon to William the coffee planter.)
My dad was Anglo-Indian (his father was Anglo-Indian and his mother was too). The paternal line was easy because the Anglo bit only went back to my g grandfather. With my dad's maternal line (the Charlesworths) it seems to go back much further, which makes it more complicated.
I've looked on the British library online records and on Familysearch, but does anyone know if there is another way of accessing East India company records? I will be going to India next year so will have a chance to do some research...
Thank you so much!
Louise