This will be regarded as a technical fault, and I'll spare you an arcane sub-discussion on inherency but this one is a fact of aviation and falls under EC261 without question to my mind. If it was caused by hailstones the size of footballs the argument starts to change, but I suspect if that was the case the OP would have compensation well down their list of concerns. If it was something like volcano dust being unexpectedly in the wrong place then BA would have a stronger argument, if it was because a vulture had crashed into the windscreen - for the first time in memory such a condor was found to be crossing the North Atlantic - then BA would not need to pay. But this is more mundane and would be in scope for EC261, and I would imagine BA won't dispute that.