On the 747 the upper deck exit is only a slide and not a slide raft so in a ditching it cannot be used unless the stairs are blocked. So customers in that area should be able to evacuate via the stairs if needed.

At LHR assistance is provided via OmniServe on behalf of BAA. They have made a huge impact over the service level provided by the previous contract holder. They still have plans to push this improvement further. One issue with assistance though is that it is not class differentiated as it is not provided by the carrier but the airport operator, so a First customer gets the same assistance as an economy one, on all carriers that operate to the UK. However as assisted customers are all taken through separate channels at points such as immigration overall the speed at which you pass through the terminal is about the same as the first ones rushing off the plane.