We had something similar - my LHR-GNB was brought forward, meaning a misconnect with my ABZ-LHR flight (5 mins short on the MCT). It was all on one PNR, and I was offered a full refund of the taxes, charges etc and the Avios redeposit fee was waived; if I'd accepted the change they would have moved me to the evening ABZ-LHR flight the day before but I think I'd have been expected the pick up the tab for the hotel, if I had willingly accepted the change.
I need to check my Amex statement to make sure they honoured the full refund...