Tim Boone, David Lewis and Nuala Smyth all travelled to Durban for the iconic Comrades Marathon, in which competitors must finish in under 12 hours.
The challenging course attracts runners from all over the world and 14,852 started the event on June 2.
Five strict cut-off times means runners must keep pace, and missing a time results in disqualification and runners not being allowed to continue, with only 10,188 finishing the race.
All three Arunners completed the race with Boone, 57, who was competing in his 113th marathon, first home in 10hrs 21mins 49sec.
David Lewis, 56, was tackling his 537th marathon and came home in 10-43-44, while 49-year-old Smyth finished her 47th marathon in 11-12-47.
Smyth said: “I was expecting it to be hard, but we were confident we could finish it. But with the temperatures and things, it’s been said that it’s one of the toughest ones so far, so obviously we were all just really pleased to have finished it.
“I have never done anything like it before in my life and it was the most running I have done in training for something.
“I had been training solid since the start of January and that was six days a week.
“There are five cut-off points along the route and they are quite brutal. If you do not make it, the stewards will cut you off.
“They will link arms when the gun goes and not let people pass. The most brutal is the last one, coming into the stadium, as despite finishing, they won’t give you a time.”
Temperatures of up to 33 degrees on the day and huge hill climbs hindered the athletes taking part in the event.
The South African runners were less affected by the conditions and the race winner, Claude Moshiywa, finished in 5-32-09.
Smyth added: “To see about 15,000 runners lined up on the start line on the day waiting to go off was just an amazing sight.
“You’re all in different pens as you have to qualify for the race, so they know what pen put you in so you’re not holding people up.
“It’s a really big event out there and, despite it being a really early start in the morning, people are out cheering on the side of the road.
“Children in pyjamas and things and it’s like a massive festival with a party atmosphere and people have barbecues and drink beer on the side of the road.
“If you run 10 of them, you get recognised and given a green number. It’s a really massive event and around 260 UK runners took part, although the majority of people that run are South African.
“They look after international runners really well, though. We had our own tent with free food and beer, if you can stomach it, and coffee at the finish line.
“It was most overwhelming to hear that people from back home were tracking us and seeing how we were getting on at different times during the race.
“To get back and know people were watching us and the support back in the UK was really overwhelming.”
Smyth, however, does not expect to ever pick up a green number due to the cost of the trip. She said: “If I lived in South Africa I would probably try, but it’s very expensive to travel out there.
“I have a family and a non-running partner and it’s quite a selfish hobby, really, but the club are very supportive.”