Indeed, congestion charge plus high parking charge in Central London do put off driving into Central London.
If people park at those shopping malls in Inner London for continuing a LU journey to central London, there’s no loss in TfL revenue, or even slightly earning as getting longer distance on TfL journeys.
Well the congestion charge is 12pm to 6pm at weekends so options for avoiding it (assuming your vehicle isn't exempt) include:
- parking on the fringes of the zone (e.g. Belgravia in the west or St Katherine Dock in the east, or round the back of Euston/St Pancras in the north) - usually free of charge, especially on Sundays - and continuing on foot or by bus;
- driving into the zone but leaving before 12pm;
- driving into the zone before 12pm, parking (again, free on Sundays in many places) and not moving your car again until after 6pm (since the charge is for driving in the zone rather than being parked in it); and
- driving in after 6pm (e.g. to go for a meal / and or to go to the theatre - parking after 6.30pm is free in the west end).
These are all tricks that are known to many Londoners and regular visitors from outside (and I would emphasise, as a Network Railcard holder living in zone 6, that Londoners aren't necessarily exempt from a dramatically negative effect of this policy on fares). When I park on London streets at the weekend it's quite evident to me that I'm not the only one doing it, but equally there is capacity for more people to do it if the incentives push them that way.
Edit: Worth adding that if there's four or five of you in one car, the tube fares multiply (especially given TfL's inability, other than through paper travelcards, to offer discounts to adult passengers travelling with a railcard holder) but the congestion charge doesn't, so it can be cheaper to just pay the congestion charge.
Even if people park a bit further out and travel in by tube as you suggest, while TfL might not lose revenue, the Mayor is still responsible for traffic congestion and air quality in places like Shepherds Bush and Stratford.
And while it's not TfL's problem if people from the Home Counties avoid London altogether and drive or take the train elsewhere (though TfL does lose revenue in that case), the Mayor is surely responsible for the local economy in London? It most definitely is his problem.
And if I, a car owner living in zone 6 near the Kent border, decide to drive to a destination in Kent rather than stay in London, in addition to TfL's lost revenue and the general loss to the London economy that's two additional car trips starting or finishing in London, which is also the Mayor's problem as he's committed to reducing the number of those.