sentences:  Welsby made just one attempt, starting his route at Heathrow and finishing at Amersham.This time was beaten on 4 May 2004 by Geoff Marshall and Neil Blake who achieved a new record time of 18 hours 35 minutes and 43 seconds.Their attempt began on the first train out of Amersham on the Metropolitan Line and ended at Upminster, and it took Guinness World Records four months to ratify it.