It is really straight forward. Thames Radar will give you vectors to the ILS. I would however note that they charge £50+ for an ILS approach, in addition to landing fees if the weather is above 5km vis / clouds higher than 1000' QFE. If weather requires you to have an instrument approach however, it is free!
That would sway my thoughts re: VFR or IFR arrival - but you may also get IFR delays in the London TMA whilst they get you over to Thames.... Just be prepared for that!
In the U.K. You could fly IFR OCAS and talk for Farnborough Radar for a deconfliction or traffic service, and bypass the delays, they will generally hand you over to Thames if you ask them to in good time.
Hope this helps!