Just out of curiousity, why not fly direct from LHR to BKK? I would choose a direct BA or QF or TJ (even in J) over going via Dubai on old Emirates F, any day. And / or can't you change to one of the EK flights with the A380 or 77W suites?
Even as an F pax the Dubai terminal is a complete dump and changing flights is a nightmare that can involve waiting in security lines for waaaayyyy too long behind a couple of A380 loads full of economy pax. No premium lanes. And boarding is the same kind of chaos all over again.
As an aside, my overall impression of Emirates after flying SYD-BKK-DXB-LHR-DXB-SYD in a mix of F and J earlier this year is that Emirates is essentially an LLC simply pretending to be a real airline. They have the same customer service ethos as Jetstar.
(Wow, I feel better now that I've got that out of my system!)