I see commuter coaches in The City lined up along Queen Victoria St. and the Victoria Embankment waiting to take commuters home. They also pick up at Canary Wharf. I don't know what the fares are but they are luxury coaches and you would be guaranteed a seat, however I do appreciate that in the amount of commuters London has, these are a drop in the ocean.
Although there's still a few into Kent, the number of commuter coach routes into London has been falling for years.