hello jasper, it was happening quite low in the sky, as the one i photographed took off from the wall, the attack initiater had just appeared above us, i think this is what spooked my one more than my presence, the one on the wall must of got about four storeys high when it took the first hit, after this i lost track of which bird was which but the action stayed at this level with attacker rising up about 20 foot or so above to set up the next attack, have attached photos of what i thought may be evidence of its presence, but not to clued up on these things so it may be from another predator.