A couple of us chatted to one of the pilots as we waited to disembark and he said it was very puzzling why the need to return to LHR when so close to the destination. The tech issue was not critical at all and very routine, they had merely requested some technical support on landing at ZRH. A return-to-base for something so routine had never happened before in his 20 years of flying with BA, seemed genuinely perplexed.