I (London residing) find that quite hard to believe.

Unless you mean TC which includes share-options "valued at" £200K+ (but likely will barely get £50k when vested after 5 years of active tenure.)

A good salary for principal engineers in London is upto £120k, but can be from half that. There are exceptional cases of higher. Highest I have personal confirmation of is £150k (a friend.)

Across all of engineering, the mean average salary at Google is £66k according to glassdoor, and that's known to be embellished.