The 22-year-old former Plymouth College pupil is joined in Stuart Lancaster’s 50-man party by fellow former Albion players Jack Nowell and Luke Cowan-Dickie.
All three were dual-registered with Albion during the 2011-12 season from Exeter Chiefs, with Slade and Cowan-Dickie also playing for Plymouth the following campaign under Nat Saumi.
Winger Nowell appears a certainty to retain his place when the squad is cut to 31 in August, while Slade’s utility is also expected to secure him a spot.
Former Ivybridge junior Slade can play fly-half, centre and full-back. He was in the Six Nations squad but did not make the final 22 for any of the games.
One player who has surprisingly missed out on a spot in the training squad is fellow Ivybridge youngster Dave Ewers. However, Lancaster has said Ewers will feature for England against the Barbarians and could still force his way into the World Cup party.
England Head Coach Lancaster said: “We are excited to name this extended squad which allows us to look at a wide group of players who have been pushing hard for selection in training with us or playing well for their clubs this season.
“It’s great to be able to include Alex Corbisiero, Joe Launchbury, Ben Morgan, Ed Slater and David Wilson, who missed the Six Nations because of injury and are close to returning to play or have recently begun playing again.
“There are a lot of experienced internationals within the squad with the likes of Chris Ashton and David Strettle, who are in great form, returning and it’s also good to have young players like Luke Cowan-Dickie, Elliot Daly, Maro Itoje and Henry Slade in there who have come through our player development pathway and had great seasons for their clubs.
“Ben Foden, Joe Simpson and Tom Croft have not been included at this stage due to ongoing rehabilitation from injury but will hopefully come into consideration nearer the tournament.
“A number of this 50-man squad, such as Joe Launchbury, Elliot Daly, Danny Cipriani and Marland Yarde will be involved in the England XV side playing the Barbarians on May 31 following the Premiership semi-finals. There will also be opportunities for the likes of Dave Ewers and Christian Wade who just missed out on the initial selection but could come back in further down the line.”
The England squad to play the Barbarians will be announced at 5pm on Sunday once the Premiership finalists are known as a number of players from the losing semi-finalists could be involved.
The 50-man group will meet up at Pennyhill Park on Monday, June 22 to begin preparing for the tournament which starts against Fiji at Twickenham Stadium on Friday, September 18.
England Rugby World Cup training squad
Chris Ashton (Saracens)
Dave Attwood (Bath Rugby)
Brad Barritt (Saracens)
Kieran Brookes (Newcastle Falcons)
Mike Brown (Harlequins)
Luther Burrell (Northampton Saints)
Sam Burgess (Bath Rugby)
Danny Care (Harlequins)
Danny Cipriani (Sale Sharks)
Calum Clark (Northampton Saints)
Dan Cole (Leicester Tigers)
Alex Corbisiero (Northampton Saints)
Luke Cowan-Dickie (Exeter Chiefs)
Elliot Daly (Wasps)
Lee Dickson (Northampton Saints)
Kyle Eastmond (Bath Rugby)
Nick Easter (Harlequins)
Owen Farrell (Saracens)
George Ford (Bath Rugby)
Alex Goode (Saracens)
Dylan Hartley (Northampton Saints)
James Haskell (Wasps)
Maro Itoje (Saracens)
Jonathan Joseph (Bath Rugby)
Courtney Lawes (Northampton Saints)
Joe Launchbury (Wasps)
George Kruis (Saracens)
Matt Kvesic (Gloucester Rugby)
Joe Marler (Harlequins)
Jonny May (Gloucester Rugby)
Stephen Myler (Northampton Saints)
Ben Morgan (Gloucester Rugby)
Matt Mullan (Wasps)
Jack Nowell (Exeter Chiefs)
Geoff Parling (Leicester Tigers)
Chris Robshaw (Harlequins)
Henry Slade (Exeter Chiefs)
Ed Slater (Leicester Tigers)
David Strettle (Saracens)
Billy Twelvetrees (Gloucester Rugby)
Mako Vunipola (Saracens)
Billy Vunipola (Saracens)
Anthony Watson (Bath Rugby)
Rob Webber (Bath Rugby)
Richard Wigglesworth (Saracens)
David Wilson (Bath Rugby)
Tom Wood (Northampton Saints)
Marland Yarde (Harlequins)
Ben Youngs (Leicester Tigers)
Tom Youngs (Leicester Tigers)