I, too have worked in Ealing (in an office block over the Broadway station).
While I agree Ealing shouldn't need the biggest of aerials in most parts, there are some places that have taller buildings that might obscure direct reception... which could allow reflections off the wings of aeroplanes on the flight path into Haethrow to mess with the signals.
There are also lots of tall, bushy trees in the Ealing streets that are now coming into full leaf. Aerials pointing through trees can have problems as the leaves can 'match' the UHF wavelengths quite successfully and block signals.
docnaz: you need to check the view your aerial has towards Crystal Palace to see if something has happened to change it recently. It would also be worth double-checking all connections are made properly - with no stray whiskers of outer almost shorting to inner - and that there are no sharp kinks or damage to the cables. Also check if near neighbours have similar reception issues.
No TVs have 'boosters' built in. Some have an 'antenna power supply' that can be switched to power an external device - but normally (almost invariably) this should be set to off.
Your description is of marginal reception. Do the LGs give signal strength and quality figures for the HD mux (and six SD muxes)? Are all the 6 SD muxes received with no errors or breakups at all, ever?