Britain's London 2012 and Rio 2016 gold medallist is set to take on the iron distance, which features a 3.8-kilometre swim, 180km cycle and 42km run.

The 42km run is an athletics marathon in its own right.

Brownlee is tentatively scheduled to embark on the record attempt between March and May in 2022, along with Norway's Kristian Blummenfelt, who holds the half-iron-distance world record.

The men's world record of 7 hours 35min 39sec is currently held by Germany's Jan Frodeno, but the pair want to break the seven-hour mark under the "Pho3nix SUB7" banner.

Attempting the "Pho3nix SUB8" on the women's side is set to be the three-time Ironman World Championship runner-up Lucy Charles-Barclay of Britain and two-time Olympic medallist Nicola Spirig of Switzerland.

Spirig won women's triathlon gold at London 2012 and silver at Rio 2016.

Both will look to better the world-record mark of British triathlete Chrissie Wellington, which is 8:18:13.

To achieve the seven-hour target, Blummenfelt and Brownlee will have to average at 51km per hour while cycling and produce a sub-two-and-a-half-hour marathon when running, it is estimated.

"We sat around a table after an endurance race in Bahrain discussing the world record times and if they could be beaten," said Brownlee.

"The women thought in the right conditions it was possible to go under eight hours.

"I thought I could go sub seven hours.

"A mix of bravado and competitive instinct kicked in and before we knew it, we had all signed up to the idea of not just attempting to go faster than anyone in history but breaking the mythical seven- and eight-hour barriers."

Chris McCormack, a former world champion triathlete and chief executive of event organiser Mana Sport and Entertainment Group, is spearheading the challenge with support from the Pho3nix Foundation, a not-for-profit organisation that supports young people's participation in sport.

"The Pho3nix SUB7 and SUB8 projects are an example to humankind that all goals - big and small - are worth chasing," said McCormack.

"They are designed to encourage young people to use sport to advance themselves for the greater good.

"What they are attempting is almost the perfect multi-sport endurance athletic challenge."

McCormack cited Kenya's Eliud Kipchoge's sub-two-hour marathon as one of those inspirational endurance feats. 

Kipchoge ran an unofficial time of 1:59:40sec in Vienna in Austria in October 2019 at a special event that included pacemakers switching in and out and lasers to indicate the ideal line and pace.