This map takes step free access data for each of Great Britain’s 2,572 main-line railway stations as listed in Knowledgebase (the rail industry’s station information database) on 3rd February 2018. (There are actually 2,563 stations – the extra 9 in the database are bizarre anomalies such as including Elephant and Castle underground station.)
There are significant accuracy problems with the information in this database, particularly on step-free access. One significant problem is that the database’s owners (Rail Delivery Group) unilaterally eradicated the “partial step-free access” category in a cost-cutting exercise a couple of years ago (without changing the database specification…). In the process they designated “partially step free” stations (with step-free access to some platforms but not others) as being either entirely step-free or having no step-free access at all, without any clear method for said re-designation. Other accuracy issues include that station operating companies (mainly train operating companies and Network Rail) are… patchy in their compliance with their licensing obligation to make sure that this information is correct, and Rail Delivery Group are patchy in their technical processes for updating the database when station operators provide this information.
So the above isn’t 100% correct in detail. However, the overall impression it gives is correct.
A better version for people with colour-blindness (sorry, I should have thought of that!)