getting it yourself in person in London can be a nightmare, firstly check that the day you go is not a public holiday in India because they will be closed.
I have over the years queued almost all day, but this year in May, midweek [Monday is not a good day] I was in and out with my visa in 3 hours much to my amazement.
It is worth paying an agency to do it for you.
Just as well they have stopped the postal visas, I saw an 80yr old man get the run round and he had sent by registered post 6 weeks before and they were so rude and unhelpful and he was flying the next day and they had lost his passport. Friends of mine sent theirs by post and a third passport came back with theirs, they returnred it to the owner but no doubt the embassy would have denied all knowledge, they seem to work in complete chaos there.