There is no London office, the London coin company are an agent who will accept submissions on your behalf, but i assume their prices would be higher, they actually do speak English in Paris, (not brilliantly) but i also spoke to their reps at the Munich coin fair in March without problem.
I've called a few times and haven't had a problem getting things corrected such as the Label on the 1862 Die letter A halfpenny, they weren't going to change the label, just make sure the coin was what it was and alter the Pop report, i insisted they change the label to recognise the variety, which they did after my call