Billy's walk was when he supported Gavin Bland on his Round in 1989.

There's a news piece attached to Gavin's ratification form: "Quick Stroll for Bill" from which:

Billy Bland of Borrowdale decided to chalk up 42 Lakeland summits to match his 42 years.
...
But Billy wasn't chasing records when he set out last weekend. He was just out for a "walk' - like Bob Graham - taking his 17 year old nephew Gavin along with him. Billy's walking pace is a little faster than most(!) - which is why he and Gavin were back in Keswick in 20hrs58mins, a fast time by any standard. According to watchers on the fells he never so much as broke into a jog.