Perhaps the concert organisers should charter trains and coaches and foot the bill for those ?
If the country/industry are serious about climate change, reducing road use/congestion, then the rail industry needs to start being more interested in extra trains/charter trains etc for the big events.
At the FA cup final, the charter train back north from Wembley left on time, despite the game running to extra time/penalties, meaning those booked on the train had the choice of leaving early to catch the train and missing the end or being stranded in London overnight as there were no other trains leaving London for the North West, the last being 8.10 from Euston. If the railways can't even let a charter train be held back until the end of the match it was there purposely for, then there's not really any hope for it.
I'm sure part of that problem is that the lines/stations affected would have had to be left open which could potentially have prevented the overnight blocks etc. That's another thing that needs attention, the early finish of the network, i.e. last Manchester airport trains leaving long before last flight arrivals, last train from Euston to North West at 8.10 etc.