The record attempt took place on Thursday 21st April, 2011, following a reconnaissance mission earlier that month. I decided to make a "small" change on the attempt day that in fact resulted in pretty much every station being visited at a different time to originally planned.
That day was chosen as Easter was a few days later, and I calculated that the network would be carrying fewer passengers than normal. The route itself was "non-standard" as it didn't use Chesham and Heathrow Terminal 5 as the two end stations, which most people do.
You can read about the day here, and watch a video here.
Here is how I proved to Guinness that I had achieved the record, which culminated in me being able to say that "Marc Gawley is a Guinness World Records Record Holder." A bit of a mouthful, but anything else and I'd be breaching their trademark. Hmm.