The Wales centre made 10 appearances for the club between 1957 and 1961 and played a dramatic role in one of the the Baa-baas' finest victories.

South Africa hadn’t been beaten by an international side in the British Isles for 55 years when they came to Cardiff on February 4, 1961.

But they were defeated 6-0 by the Baa-baas with Mainwaring — a late call-up at full back — denying the Springboks with bone-crunching challenges on lock Avril Malan and wing Michael Antelme. 

The Sunday Times described his try-saving clash with South Africa captain Malan — a dramatic shoulder charge on a bigger opponent — being "like a comet burying itself into earth". 

“As a player Haydn Mainwaring was extraordinarily courageous and he will be famed forever for that tackle on the South African captain,” said Barbarians’ President Micky Steele-Bodger.

“He was a very sound and versatile player, a marvellous all-round games player and such good company that people always wanted him to be part of their team. He had big heart and was great fun to be with. 

"He went on to serve on the club’s committee with distinction and our sincere condolences go out to his wife Eryl and their family."

A Royal Marine, Mainwaring played for the Royal Navy, Combined Services and a number of clubs including Harlequins, London Welsh, Swansea and Newport.

Equally at home in the back row and centre, he made his debut for the Barbarians on the 1957 Easter Tour at full back in a side captained by Cliff Morgan. 

He was in exalted company against South Africa when the Barbarians team included giants of the game in Tony O’Reilly, Syd Millar, Richard Sharp, Ronnie Dawson. Two Morgans in the back row — Wales’s Haydn and England’s Derek — scored the tries that day.

After retiring Mainwaring was a Barbarians committee member representing Wales’s interests on the club’s board from 1989 to 2008 and he was made a vice president of the club in 2012.