The other thing if you go to Hatton Cross is take the bus back to T5 from there. For the first time in ages I got driven to T5 last week as the sun was setting. The terminal at the time of the evening almost seemed to float (or maybe that was all the Guinness at the rugby).

Would also recommend then science museum as they've a cut out of a 747 fueselage there if you have the time. And it's on the Piccadilly line to LHR.