knobbygb, I regret to say that I do not know the definitive answer and so presume the worst - that each party will blame the other! This view has been developed after 20 years in telecommunications where the 'law' states that if one company connects a circuit/device to another company, then it is
always the
other company at fault ...
Glad to hear that you found an airline that would do the decent thing. For my part (and when asked by friends or colleagues who know that I travel a lot) I prefer to have the hassle of reclaiming the bag at the mid point.
It has been my good fortune (and planning!) that I have lived within 35 miles of LHR for the last 20 years. Consequently, I very rarely have to change, at least when in travelling within Europe.