Before the usual crowd of BA regulars jump in to tear their hair and wail about how it's the worst airline EVAR, I'll see if I can give you some useful information:

- Your flight will be on the new A340-600, with BusinessPlus seats. Grab row 1 or 6 and you'll get a flat bed (the other rows are slightly angled) that most people think is pretty comfortable. It's a standard seat, not anything creative like you'll find on BA, VS, NZ, or (now) UA.
- Food on the long-haul is pretty much the same as all business class airplane food I've ever had (though not as bad as KL science experiments).
- Service is professional, though don't expect crew to go out of their way for special requests or grin like an ape every time they speak to you.
- IFE is good.
- Lounge in MAD is very good. Not quite as nice as a Terraces but a good place to spend some time.
- The LHR-MAD flight will be comparable to BA, except you'll be 2x2 on an Airbus and not 3x2. I think the food on the IB short-haul is better than BA, but that may just be my pallette.

I have limited experience with both BA and IB long-haul, just a couple of flights each. I thought they were pretty much comparable, and completely survivable. On the other hand, I've done the LHR-BCN or LHR-MAD flights on BA and IB about 30 times each, and have absolutely no preference either way, except I prefer the BA lounge in LHR to the IB one.