From the Southern Travellers Handbook for 1965/66 #4
For the Southern [region], meeting this demand requires a total of 7,000 trains a day running 60,000,000 miles a year. More than a quarter of these trains run in the two short peak periods of each day. A bird's eye view of the south east in the rush hour would show a fascinating picture of green streaks seperated by less than a mile all moving, as if drawn by a magnet, towards the centre.
Between 08.10 and 08.20 no fewer than 37 trains every minute are converging on London, most of them running on a two-minute gap between trains and their timetables worked out to the second - 20 seconds is, in fact, the waiting time allowed at most stations.