Run for It

Britain is such a small island that it is possible to run across it in one day. 

If you were able to run at a top human speed you can get anywhere in Britain in 10 hours. No one can though, most humans can only sprint for 2 minutes. 

If you jogged at half the sprinting speed 20km/h or 12 to 14 miles per hour, you could run to any part of Britain in a day. Animals that run fast like horses can't maintain a human jogging speed for long, they would just collapse after a few hours so humans are the fastest long distance runners on earth.