Not seeing WFH drastically reducing car use. Those who did commute by car will be used to the convenience of shopping/visiting at short notice by car on way home, many of those who used to commute by public transport will find they need a car for all those things they used to pop out at lunchtime for or pick up between the office and the station.
I've explained this before.
If there's two people who commute to work by car and they then WFH 2 days a week they can then use one car for 4 out of 5 day a week. In that case what is more likely, one person then using public transport one day a week or having a second car which is only needed a few times a week?
Chances are there'll be quite a few who will opt for the public transport option. Not everyone certainly but enough that it would offset much of the losses from the trains.
As I've said before 80% is by car and 10% is by rail. Even a 20% drop in rail use (2% of the total, or the same as everyone who uses rail working from home 1 day a week) would only need 12.5% of car use to switch to rail 1 day a week (2% of the total) to keep rail at its previous levels.
That still leaves households with the option of just popping out for the vast majority of their travel, however there could be times when they'd have to plan ahead a bit more and use public. However that would likely be the minority of case and so probably wouldn't make a significant impact on their ability to go about nearly the same as before.
As I've said that won't be everyone by a long way however there'll be other people for whom for other reasons that they could reduce the numbers of cars that they own, which would also increase rail use occasional.
There's also going to be those who struggled with continuing to pay for their cars whilst their neighbours day at home with much reduced outgoings due to not paying their public transport season ticket costs and wondering what happens if there's a second wave or a different Pandemic? Would they not be better off using other modes of transport. Especially given that office workers are likely to be amongst the last to be released from their restrictions.
If this goes on for 9 months then that's 1/4 of the time of a 3 year car lease which people would have been paying £100 to £200 maybe even £300 a month and not really being able to use it enough to justify that cost. There's going to be quite a few who just don't renew their leases until this is all over. Even 20% of petite with leases not renewing that a 5% drop in lease cars on the roads. Now many of those will restart once this is over but there'll be quite a few who won't.