Six Nations 2013: England include Billy Twelvetrees and Calum Clark

Uncapped pair Billy Twelvetrees and Calum Clark have been named in a 33-man England squad for the Six Nations.

Gloucester centre Twelvetrees, 24, has forged an effective club partnership with Freddie Burns, who is one of three fly-halves in the squad.

Northampton flanker Clark, 23, served a 32-week ban last season for breaking Leicester hooker Rob Hawkins's elbow.

Burns, lock Joe Launchbury, hooker Tom Youngs and prop Mako Vunipola are formally promoted to the senior squad.

England kick off their Six Nations campaign against Scotland at Twickenham on 2 February.

The requirement for an eight-man replacements' bench means senior squads have been increased to 33 players, with Vunipola the additional prop.

Head coach Stuart Lancaster is confident Clark has learned his lesson from the Hawkins incident and that he has both the temperament and the ability to succeed at the highest level.

"He has been harnessing the competitive nature he has got, which you want in players to win games, but he is channelling that in the right way," said Lancaster, who coached Clark when he was at the Leeds academy.

"He has had tough lessons to learn. I have coached him since he was 14, I probably know him better than most.

"I know what he can offer. In addition to his desire to win, his versatility in the second row is an option for us. He is incredibly athletic and very good in the contact areas."

In March, Clark pleaded guilty to injuring Hawkins in the LV Cup final and was banned from 22 March to 1 November, ruling him out of England's summer tour plans and the autumn internationals.

With Wasps lock Launchbury, 21, also included, both Mouritz Botha and Tom Palmer drop out of the squad.

Saracens wing David Strettle has been recalled, with Gloucester's Charlie Sharples dropping out, while Leicester flanker Tom Croft, who only recently returned after neck surgery, is also included.

Wasps back-row James Haskell is preferred to Phil Dowson of Northampton, who drops into the second-string Saxons squad.

On Tuesday, Leicester fly-half Toby Flood was cleared to play in the Six Nations after a citing for an alleged tip tackle was dismissed at a Rugby Football Union disciplinary hearing.

He was cited for a dangerous tackle on Worcester counterpart Andy Goode in the Tigers' 19-14 Premiership win.

Twelvetrees replaces Leicester's Anthony Allen, Burns takes over from Harlequins' Jordan Turner-Hall, and Leicester's Youngs replaces injured Bath hooker Rob Webber.

Burns, Launchbury, Youngs and Vunipola were officially acting as injury cover when they helped England to a record 38-21 victory over the All Blacks in December.

"It was a tight call between Billy Twelvetrees and Anthony Allen but we wanted to get a chance to work with Billy," said Lancaster.

"The opportunity for David Strettle has come alongside a move to the left wing [at Saracens]. His form has been outstanding but Mike Brown was fantastic there against the All Blacks."

Vunipola's younger brother Billy, the Wasps number eight, will train with England in their pre-Six Nations camp in Leeds later this month as cover for Croft.

Wasps wing Christian Wade and Bath's former rugby league star Kyle Eastmond are in the Saxons squad, which also includes another league convert in Saracens centre Joel Tomkins.

The Saxons play the Irish Wolfhounds on 25 January and Scotland A in Newcastle on 1 February.

England senior elite player squad:

Forwards: Props: A Corbisiero (London Irish), D Cole (Leicester Tigers), J Marler (Harlequins), M Vunipola (Saracens), D Wilson (Bath Rugby); Hookers: D Hartley (Northampton Saints), T Youngs (Leicester Tigers); Locks: J Launchbury (London Wasps), C Lawes (Northampton Saints), G Parling (Leicester Tigers); Back-rows: C Clark (Northampton Saints), T Croft (Leicester Tigers), J Haskell (London Wasps), T Johnson (Exeter Chiefs), B Morgan (Gloucester Rugby), C Robshaw (Harlequins), T Waldrom (Leicester Tigers), T Wood (Northampton Saints).

Backs: Back three: C Ashton (Saracens), M Brown (Harlequins), B Foden (Northampton Saints), A Goode (Saracens), D Strettle (Saracens); Centres: B Barritt (Saracens), J Joseph (London Irish), M Tuilagi (Leicester Tigers), B Twelvetrees (Gloucester Rugby); Fly-halves: F Burns (Gloucester Rugby), O Farrell (Saracens), T Flood (Leicester Tigers); Scrum-halves: D Care (Harlequins), L Dickson (Northampton Saints), B Youngs (Leicester Tigers).

England Saxons elite player squad:

Forwards: Props: N Catt (Bath Rugby), P Doran Jones (Northampton Saints), S Knight (Gloucester Rugby), M Mullan (Worcester Warriors), H Thomas (Sale Sharks). Hookers: J Gray (Harlequins), D Paice (London Irish); Locks: M Botha (Saracens), L Deacon (Leicester Tigers), G Kitchener (Leicester Tigers), T Palmer (London Wasps), G Robson (Harlequins); Back-rows: P Dowson (Northampton Saints), W Fraser (Saracens), M Kvesic (Worcester Warriors), E Slater (Leicester Tigers), B Vunipola (London Wasps).

Backs: Back three: N Abendanon (Bath Rugby), T Biggs (Bath Rugby), K Eastmond (Bath Rugby), J May (Gloucester Rugby), U Monye (Harlequins), C Sharples (Gloucester Rugby), C Wade (London Wasps); Centres: A Allen (Leicester Tigers), E Daly (London Wasps), G Lowe (Harlequins), J Tomkins (Saracens), J Turner-Hall (Harlequins); Fly-halves: G Ford (Leicester Tigers); Scrum-halves: J Simpson (London Wasps), R Wigglesworth (Saracens).