The high salaries paid in London though would suggest that they aren't just passing on IP developed in Mountain View. There has to be some value-add there or they wouldn't earn an average of 160k each.
They are executing the business model from Mountain view. They are analyzing results and modifying strategies for successful UK operation, and handling localized issues.
That is not revenue generation.
Take a supermarket as an example.E.g., Tesco decides what products to sell, negotiates with supplies, sets prices, manages marketing, develops new products etc. A single store just executes the business model. the actions of the manager have little to do with the Tescos corporate business, but Tescos wants to hire good store managers and that might require good pay.
The google guys in Lodon are trying to maximize the profits, but they don't generate revenue, Google IP does.