Yes, thanks. I know a new / better / properly aligned aerial will be better, but also a nuclear option that I am trying to avoid for reasons stated above (three storey house, on the coast, in a wind tunnel, cement board cladding, all internal cabling hidden in the walls).
I couldn't find a Proception DA with the DC power back to the masthead amp, but I have found an Antiference one that looks good, it is 8 way, has the DC power, and has built in attenuation, it's also got a returns option, so I am going to give that a try and see if it makes any difference.
The Freeview postcode checker - detailed view, shows Com 7 at 64% from Crystal Palace, and 97 / 98 % from Bluebell Hill. But they are both the same frequency, (55 / 746) so I don't know where it's coming from either.