The 22-year-old Twelvetrees has made 14 appearances for Leicester Tigers this season, mainly at fly-half, and has contributed 139 points in league and cups.
Twelvetrees joins the Saxons squad after Sale Sharks fly-half Charlie Hodgson was elevated to the senior squad for the RBS 6 Nations.
England Saxons head coach Stuart Lancaster has made six changes to his squad, with forwards Joe Marler, James Gaskell, Dave Attwood and Christian Day being joined by Twelvetrees and Northampton Saints centre Jon Clarke. Saints lock Christian Day is an injury replacement for Leicester’s Geoff Parling.
Twelvetrees is joined in the squad by Tigers colleagues Jordan Crane, Anthony Allen and Dan Hipkiss who have all been capped at senior level.
The Saxons face Italy A at Worcester on Saturday, January 29 (3.15pm) and Ireland A in Belfast on Friday, February 4 (7.30pm).
Temporary injury replacements for prop Matt Mullan (Worcester), hooker Rob Webber (Wasps) and Dan Ward-Smith (Wasps) will be named later this month.
ENGLAND SAXONS EPS
Forwards
Steffon Armitage (London Irish)
David Attwood (Gloucester Rugby)
Duncan Bell (Bath Rugby)
Steve Borthwick (Saracens)
Alex Corbisiero (London Irish)
Jordan Crane (Leicester Tigers)
Christian Day (Northampton Saints)
Phil Dowson (Northampton Saints)
James Gaskell (Sale Sharks)
Joe Marler (Harlequins)
Lee Mears (Bath Rugby)
Matt Mullan (Worcester Warriors)
Luke Narraway (Gloucester Rugby)
Chris Robshaw (Harlequins)
Andrew Saull (Saracens)
Dan Ward-Smith (London Wasps)
Rob Webber (London Wasps)
Tom Wood (Northampton Saints)
Backs
Nick Abendanon (Bath Rugby)
Anthony Allen (Leicester Tigers)
Brad Barritt (Saracens)
Jon Clarke (Northampton Saints)
Alex Goode (Saracens)
Dan Hipkiss (Leicester Tigers)
Paul Hodgson (London Irish)
Ugo Monye (Harlequins)
Stephen Myler (Northampton Saints)
James Simpson-Daniel (Gloucester Rugby)
Mathew Tait (Sale Sharks)
Billy Twelvetrees (Leicester Tigers)
Dominic Waldouck (London Wasps)
Richard Wigglesworth (Saracens)
