In the past, I traveled w/ one fold out/up type single outlet adapter (maybe from Targus) and plugged an AC power strip into that, then all my various wall warts/charger blocks into the power strip.
Via Amazon I bought this
BESTEK Universal Travel Adapter 220V to 110V Voltage Converter with 6A 4-Port
USB Charging and UK/AU/US/EU Worldwide Plug Adapter
and am going to give it a try in a week or so when in LHR.