Similar position as you - distant learning whilst in full time job. I was initially looking at BGS but then their revision weeks are split into 2 x 2 week courses...meaning 4 weeks off work in total, which I couldn't do.
Cranfield (CATS) on the other hand do it in 3 x 1 week courses so only 3 weeks off needed. Plus the fact that you can't beat them on price (£999 is their cheapest option, compared to £2100 for BGS).
So to compromise I went with CATS and bought some second hand BGS manuals to support my studies. Oh and of course used their question bank before exams.
The results so far - 99% average with 4 exams to go.