@Mark1065 As a fellow London host I certainly understand the problems we are currently having with the weather but you are charging £225 per night and for that, if I were your guest, I would expect to be kept cool. As for the noise issues - of course the guest should have realised in advance that the centre of London is not a country village and expected the noise from all night buses, busy restaurants etc - but I think you should mention the potential for noise in your listing, to cover yourself if nothing else. The noise is the same all year, whereas this heatwave is temporary.
As far as the early check in is concerned, you need to establish in advance at what time the guest will arrive, and this can only be done via good communication. If the guest wanted to arrive early in the morning you could have made sure that he had booked the previous night as well. I always ask guests who are coming from far away - Australia, NZ, USA, Canada, Africa etc - for their flight details so that I can check what time they arrive at LHR.