Clearly, many of them would become unemployed.
The job I accepted was one where there is a bus service. That service takes five times longer to get there than by car if you leave by 6.30am. If I were travelling during standard commuting hours, a car would take about 4 minutes longer, but the buses would either fail to stop because they were full from 7.15-9.25am and if they did, the journey time increases to 'well, you'll get there at some point this morning, unless there are roadworks or an accident - in which case you might as well not bother'.
I didn't accept the better paid job that meant 2 buses where the services are regularly cancelled at the first hint of weather due to the terrain and then a 45minute walk up a selection of steep hills, including a 25% one, or a 25minute walk across deserted fields in the dark from October to March. And countless others where I didn't apply in the first place because it's either clear they impossible to get to or where they put down 'due to the location, it is essential that applicants have a full driving licence and their own transport'. There are many locations within a 10 to 30 minute drive of this part of Greater London which literally have no public transport, so might as well not exist for people who are poor and looking for work or who are disabled (before you tell me it would be easy for anybody to cycle), even if you ignore the journey time of 25 minutes by car compared to 2h45m by walk, wait, bus, traffic jam, wait, train, train delay, wait, train cancellation, wait, train, delay outside the station, walk, get threatened with the sack for not getting up in time to get to work because it's 9.25am and you left the house just after 6.
When you can get from London to the West Country in the time it takes to go less than ten miles (and can't ride or don't want to become another news item about a woman killed whilst cycling - there's a good reason why those reports rarely saying 'leaving two children' - mothers don't want their kids to have to grow up without them), many, many people do need cars to get and keep jobs even in Greater London.