`utterly appalling record of the British army in Spain`
You refer to the sieges and storming of Cuidad Rodrigo, Badajoz and San Sebastian?
Those were three isolated exceptions of rampant indiscipline, all after very bloody stormings, which Wellington and his officers stamped on as quickly as they could.
I suggest you take a look at the record of the French armies all over Spain and in northern Portugal, on a daily basis, for five years. `Get over yourself`?