The PC British layout is annoying. It swaps @ and " relative to the US layout, among some other important keys, which means that when you're dropped at a US-layout terminal you struggle.
It also doesn't have the wonderful set of Alt+ combinations as the Mac British layout for typing various types of diacritics, widths of dashes, Greek letters, mathematical symbols, opening and closing quotes, and other things. PC layout users are stuck with acute accents, the Euro symbol, and nothing else.
Luckily, the Mac "British - PC" layout (not the same as the actual British PC layout) does include the extra Alt+ combos.
I'm not sure why anyone would find the Mac British layout difficult to program with. It's closer to the US layout than the PC British layout. I suppose # requiring Alt might be bothersome, but # isn't a symbol used that frequently in programming, and Alt+3 is not that difficult to type.
Having always used a standard british keyboard, the subtle differences, e.g. location of \, #, ", `, ~, really slow me down. It just seems petty for Apple to ignore the standard and go it's own way... then again, it is Apple.
Also, I use # loads every day for c++ macros, and #if 0 blocks.