I can tell it's not accurate because it has half the trains marked as on time.
Reality is far more depressing. You'd also need to add ghostly white for cancelled and bus icons for replacement buses. Why do I live here god. Why can't we have a functional train network like literally any other civilised country.
More than half of British trains do run exactly on time (within the scheduled minute). It's quite high — over 65%. Over 85% arrive within three.
It's a bit massaged in some cases e.g. Transpennine, who have only recently been forced to stop abusing P-coding to pre-cancel trains that would have been significantly delayed. So I think those figures may take a dip.
But re: civilised countries: Germany's rail service is effectively significantly less punctual than ours; regional services are OK, about as good as ours, but if you need a longer haul service for any part of your journey you will have a very much worse experience. France is a bit more punctual on long-haul, I think; they average better within-the-minute punctuality on TGV, but regionally it is not better than the UK, it is worse. Italy (in some senses the most civilised country on earth) has poor train reliability.
Delays on UK networks are in many case due to very fundamental, long term issues that are hard to resolve. Rural lines that are single-track for geographic reasons, for example — where it's a choice of either single track or no train. And there are some absolutely pathological problems like the Borough Market Junction, which has been a cause of severe structural delays for about 140 years, in part because the only way to solve it is to destroy historic parts of London.
I personally do not think delays are the biggest problem in UK rail; ticket prices are. The slow return of train services to various forms of public ownership may help there, but we need the ROSCOs too. We need to stop what privatisation did. Perhaps we will.