Yes R33, I assume that distinction is meaningful in the UK, in the US, lower middle class and working class are used more or less interchangeably these days as a result of there not really being much of a middle class any more.
Merrick's backstory in the book is that his father was a somewhat successful shopkeeper but that both parents died when Ronald was a teenager, and he was taken in by the headmaster of his grammar school, who, knowing he was very bright and might have been able to go on to university had his father not died, helped him secure a job in the Indian police where it was thought that his background would not work against him the way it would back home.
This seems clearly meant to contrast with Hari Kumar, who was also orphaned, but was not taken care of by anyone in the Chillingborough community and found himself back in India. Hari had assumed (as did the other Chillingboroughians) that his Indian relatives would agree to resume his education, but they did not and he was too proud/embarrassed/shocked to ask any of his friends , classmates or teachers back in England for help.
Daphne Manners is also an orphan--her father and brother were killed in the North African campaign, but she is taken in by her wealthy aunt, Lady Manners.
Guy Perron is also an orphan--his parents died when he was very young, but he was raised by a collection of eccentric and unmarried aunts and uncles.
Ditto Barbie Bachelor, who becomes a missionary upon the death of her parents.
Scott seemed to be making a point about how the upper classes take care of their orphaned relations, providing them with the same opportunities and privilege, while Merrick and Kumar were both thrown off track by their parents' deaths.
Thinking about it, a paper examining Scott's use of orphanhood in the Raj Quartet would make an excellent undergrad thesis.
Oh well, next time I'm in college ;)