Backs coach Mike Catt said he had been extremely impressed with Lamb's attitude and skills in training.
Farrell will line up alongside the veteran centre Mike Catt, 35, who has plenty of experience at fly-half.
Lamb said he was looking forward to working with Booth and Mike Catt.
The visitors introduced former England centre Mike Catt at fly-half, with Geraghty shifting to inside centre, on the hour mark.
England will not name his replacement until Friday, with Olly Barkley, Mike Catt or Dan Hipkiss set to come in.
The Saracens player will start as England's first-choice goalkicker, and will share the responsibility of playing at fly-half with Mike Catt.
Mike Catt, the English rugby team's fly-half, grew up in South Africa.
In the 14th minute Mike Catt's attempted drop attempt curled wide and seven minutes later the Springboks went desperately close to adding another try.
Corry is the fourth former England captain to stand down since the World Cup, following in the footsteps of Jason Robinson, Lawrence Dallaglio and Mike Catt.
Ashton, 61, defied the odds to guide England to the final in France, but his management style was criticised by senior players Mike Catt and Lawrence Dallaglio.
Tomas De Vedia (2), Mike Catt and Delon Armitage secured the crucial four tries inside half-an-hour, before the shell shocked home side got a Mike Owen try.
London Irish welcomed back England fly-half Shane Geraghty, though Mike Catt and Andy Farrell were still injured, but the 20-year-old endured a torrid return from the Six Nations.
Olly Barkley is expected to replace Stuart Abbott in England's midfield, with Mike Catt or Fraser Waters the alternatives if Mike Tindall does not recover from his latest injury setback.
The positions of Jamie Noon and Mike Catt will come under scrutiny, as will that of Dallaglio, while Jonny Wilkinson's fitness or otherwise will be determined in the next 48 hours.
To have someone like Mike Catt, which I didn't have at Gloucester, who's an out-and-out (number) ten and can take me through exactly what they want from a fly-half, is fantastic.
Alternatively, Ashton might decide to start with Mike Catt or Andy Farrell at number 10, with the other playing centre, although he would then have no back-up fly-half cover on the bench.
Martin Corry, Jason Robinson, Mike Catt and Lawrence Dallaglio - all former England captains with 275 caps between them - have retired from international duty since England's run to the World Cup final last year.
England's injury crisis forced them to select veteran centre Mike Catt at fly-half against South Africa, with a brief to share the duties with rugby league convert Andy Farrell, who was named as the goal-kicker.
He will compete for the inside centre jersey with Mike Catt, 36 next month, who will equal Jason Leonard's England record of being selected for four different World Cup campaigns - 1995, 1999, 2003 and 2007.
The others are captain Phil Vickery, Mike Catt, Jason Robinson, Josh Lewsey, Jonny Wilkinson, Andy Gomarsall, Mark Regan, Martin Corry, Ben Kay, Lewis Moody and Joe Worsley, while Simon Shaw was a replacement but did not play.
That late Evans penalty put paid to a late rally from London Irish, but it was all a bit too little, too late from the hosts, for whom Mike Catt had an off day with the boot.
Since that day, Jonny Wilkinson has returned to the side at fly-half and formed an effective combination with Mike Catt -- he is expected to shrug off a groin problem -- while the likes of Simon Shaw and Andrew Sheridan have been inspirational up front.
Woodward's decision to include the larger of the two Mike's - Tindall over Catt - is applauded by most papers, including The Telegraph .
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