The new club will be known as London Irish and will share the Stoop ground with Harlequins. The London Irish chairman, Geoff Read, said the club's new strip would incorporate the colours of all three original clubs and would be coached by the former London Irish coach Dick Best. "We're a new club in a new home and we'll offer an exciting blend of the talents and traditions of all three clubs," Read said.
The merger was proposed after Richmond and Scottish hit financial difficulties. As a result, next season's top division has been reduced from 14 to 12 clubs, although that development is being contested through the courts by Rotherham.
The Premiership Two club are seeking an order forcing English First Division Rugby to comply with terms of the Mayfair Agreement - English rugby's peace document - and two Premiership divisions of 14 teams. Rotherham missed out on promotion last term, beaten by Bedford in a play-off, and their fight will go to the High Court in London on 16 August.
EFDR intends to mount a vigorous defence, and the chief executive, Howard Thomas, welcomed confirmation of the merger. "The deal the three clubs have put together builds a strong and secure super club ready to compete at the highest level with an excellent support base," Thomas said.
Best's squad will comprise very few Scottish or Richmond players, though, the overwhelming majority having already been signed from other clubs at home and abroad.
Meanwhile, Northampton yesterday completed the signing of the Argentine international Martin Scelzo on a two-year contract. The 21-stone prop will join after the World Cup.
Newport have unveiled their latest signing, the South African centre Andy Marinos, who has agreed a two-year contract. Marinos, who played for Western Stormers in this year's Super 12, could even help Wales gain a World Cup place. He qualifies through his grandparents, and has had discussions with Graham Henry.
Henry has announced his 30-man World Cup squad, but a vacancy could crop up if Australia's Jason Jones-Hughes loses his appeal next month against an International Rugby Board decision blocking his Welsh ambitions.
n A Welsh XV likely to feature non-first team players will tackle the United States at Cardiff's Millennium Stadium on Bank Holiday Monday, 30 August, two days after Wales play France.