Richard J. wrote:

Last train from Hyde Park Corner to Cockfosters is at 00:31.

After that, you'll need to make your way to Trafalgar Square (a short walk,
or a night bus ride), and then get night bus N91. This runs all night to
Cockfosters, operating every 20 minutes on a Friday night, and will accept
your one-day Travelcard (which would be issued at Cockfosters in leiu of a
return tube ticket) until 0430.


MG