Hi FlyBy
I did a fair chunk of, and completed, my PPL with Firecrest. I found them to be a friendly operation and reasonably efficient with decent instruction. Compared to Cabair they are a little shabbier in terms of presentation, Cabair has a very nice office and a fleet of smart newish aircraft, but then its questionable how important these things really are.
There is another outfit at Elstree, Flyteam, I'm not sure if they still do instruction from Elstree.
Overall Elstree is a good place to learn at as it has a shortish runway and can be very busy - all good experience. Depending on where you nephew is he might also want to take a look at Stapleford as well, I don't have any personal experience of them but they seem quite professional.