The hugely popular Outlaw Half event has already sold out, taking less than 24 hours for all 1,360 general entry tickets to be snapped up for the June 2014 race around Nottingham.
Iain Hamilton, founder of organisers One Step Beyond, commented: "This is the second year of the Outlaw Half and last year it sold out in four days, so this is quite overwhelming!"
Hamilton added that there are still around 100 tickets available through Cancer Research (call 0871 641 2403) or through sponsor and media competitions that will come up during the year.
Demand is slightly lower for the full Outlaw event (3.8km swim/180km bike/42km run) taking place next July, with around 400 places left at 10.15am today (28 August, 2013), according to Hamilton.