They offload the bags.
They've had huge success at getting in new throughput but the customer experience is now a shopping mall on a busy Saturday and getting claustrophobic. This is a typically British approach as the balance between commerce and experience swings too far towards the mighty £. It's like Heathrow in the last decades of the 20th century, just bolting new bits onto a structure that was never designed with such volumes in mind.
Needs rebuilt from the ground up but would there be a good ROI in such a market?