I just checked BBC online, 1940 in the evening, It looks like they're still trying to find a way to break the "bad news" about the low turnout (still speaking of it as a future event-----at 20 minutes before 8 pm!). It sounds like they're piddling in their pints.
Their story includes the interesting tidbit that many London schoolchildren are expected to be released for the protests. So the number of REAL protesters, is even lower!!