The two clubs have established close links over the last few years, as befits two sides whose training grounds are only about three miles apart - but it has taken over 100 years of history to establish those links.
Welsh were founded in 1885; 18 years after Wasp. During the amateur era, both were among the cluster of senior clubs based in the London area who enjoyed a regular and friendly, but keenly-contested, rivalry. In this period Welsh were one of the glamour sides reaching their zenith in the late ‘60s and early ‘70s, under the inspiring captaincy of John Dawes.
However by the time the first leagues were formed in 1987/8, Welsh had slipped from the top level of English club rugby and while the Wasps sting began to gather more venom, the Welsh dragon began to lose its roar, and the Exiles soon slipped to the obscurity of league rugby several levels down from the top tier – Wasps and Welsh were, quite literally, leagues apart.
Gradually, the sleeping dragon began to stir, and the famous old club began to find its way back towards the top and it was once they were back in the Championship that the closer links with Wasps were set up.
London Welsh has provided an ideal place for young Wasps players to develop, through dual registration – amongst them Hugo Ellis and, more recently, Nathan Morris. Meanwhile, Welsh provided the Wasps A team with a steady stream of players – England prop Paul Doran-Jones made some telling appearances for the Wasps second string in one of its championship-winning campaigns.
A series of former Wasps players have moved on to London Welsh after taking off the Black and Gold colours. The first of the professional era was Florent Rossigneux and soon after Rossigneux came a flying winger, who was to establish himself as one of the most outstanding players in the recent history of London Wasps - Paul Sampson.
Other former Wasps who followed him to Welsh included Ben Gotting, Tom French and Edd Thrower.
It was two former Wasps who finally helped turn London Welsh from a solid Championship side to a real promotion contender. Phil Greening and Mike Friday were the Welsh coaches when they reached the 2011 play-off semi-finals, where they lost to Cornish Pirates (coached by another ex-Wasp, Harvey Biljon!).
Sunday’s game itself is something of a homecoming for several London Welsh players and coaches.
Included in the Welsh coaching team is Simon Amor, who is in charge of the London Welsh scrum-halves. A sevens specialist, Amor spent two seasons at Wasps, and his experience and expertise helped them win the Middlesex Sevens in 2006 – their first title since 1993.
One of the most recognisable members of that triumphant Gatland squad was lock Martin Purdy. He spent seven years with Wasp s and played a big role in the triumphant Heineken Cup campaign of 2003/4.
Alongside him in the second row is another former Wasp, Matt Corker. Matt was named Wasps Young Player of the Year in his first season, 2005/6, when he also made his first team debut. He was a regular in the championship-winning 2006/7 A team, which also beat the first team in a warm-up match, ahead of the 2007 Heineken Cup final.
More recent Wasps in the Welsh line-up include Ryan Davis and Seb Jewell and London Wasps A team regulars will recognise the muscular frame of winger Joe Ajuwa, who has made a number of appearances for the Wasps second team.
In addition to those players, young Wasps prop Lewis Thiede and Jonah Holmes were both on loan to Welsh recently.
As we all know, Welsh finally made it to the top tier last season. While that decision means that the links between Wasps and Welsh cannot be as close or cosy as they have been in recent years, the Clubs will remain close friends and neighbours.
This is an extract from a longer feature in this weekend’s match programme
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