Both teams go in to this match needing a win to keep alive their semi-final dreams. England also need to score four tries and collect a winning bonus point to stay in contention - and Lamb will drive them forward from stand-off, while Allen starts in the number 12 shirt.
Mallinder said: "We've made six changes to the team that played New Zealand. In a demanding tournament situation like this rotation is important to give everyone a balance between rest and game time, especially after a hard match against New Zealand.
Matt Cornwell returns to the midfield and resumes the captaincy after recovering from injury. Sale Shark Ben Foden also takes his place in the starting team after proving his fitness on Tuesday from the bench.
Sixways speedster Uche Odouza earns his first start after making his debut from the bench in the last match. Odouza will fly home after the match to sit an A level exam at St Edmunds in Wolverhampton before rejoining the squad in time for the next round.
Mallinder added: "This is a tough but vital match for us. After the disappointment of New Zealand the boys are all looking forward to playing again. We've very keen to progress and to do that we know we need to win, and win well."
The match will be played at Riom, near Clermont Ferrand, about an hour from the team's Vichy base. Kick off is 6pm local time.
England Under-21: Mike Brown (NEC Harlequins), Topsy Ojo (London Irish), Matt Cornwell (Leicester Tigers) captain, Anthony Allen (Gloucester), Uche Odouza (Worcester Warriors), Ryan Lamb (Gloucester), Ben Foden (Sale Sharks), Alex Rogers (NEC Harlequins), Chris Brooker (Bath Rugby), Mark Lambert (NEC Harlequins), Tom Ryder (Saracens), Richard Blaze (Worcester Warriors), Chris Robshaw (NEC Harlequins), Michael Hills (Sale Sharks), Jordan Crane (Leeds Tykes) Reps: Rob Webber (London Wasps), David Wilson (Newcastle Falcons), James Haskell (London Wasps), Iain Grieve (Bristol Rugby), Danny Care (Leeds Tykes), Ryan Davis (Bath Rugby), Matt Riley (Sale Sharks)