Bath's Ryan Davis replaces Allen in the centre, while Newcastle's Toby Flood gets a start at stand-off in place of Lamb.
The match was originally thought to be against Ireland but the IRB has confirmed that England, who finished fifth behind New Zealand on points difference, will play eighth place Wales.
The match takes place tomorrow, Wednesday 21 June, at 17.00 in Vichy. It is preceded by Ireland v Argentina, who finished fifth and sixth after the pool matches. The winners of these two games meet in the final round on Sunday to decide who will finish in fifth place overall.
Mallinder has handed Matt Riley, Sale Sharks, and Bristol's Iain Grieve their first starts. "Matt came on for us against New Zealand and did a good job. Although Iain only got a few minutes against Scotland, his attitude in training and his performances for England Under-19s this year have been outstanding and he fully deserves this chance."
Davis will get his first chance of the tournament. Although he was not involved in this year's Six Nations, the Bath centre was an important part of the 2005 Six Nations squad before injury ruled him out of the Under-21 World Championship later that season.
Mallinder added: "It's a big ask to play five tough matches in 17 days and we're very lucky to have a fully fit squad to select from. We've had two very physical matches on the bounce so it's important to bring in fresh legs. We know that Wales will be another difficult match for us.
"The loss to New Zealand was our first defeat of the season and our goal for the two remaining matches is to keep that record. Nine wins from ten games is the best we can do now and that is what the boys are playing for," he said.
England Under21s: Mike Brown (NEC Harlequins); Topsy Ojo (London Irish), Matt Cornwell (Leicester Tigers) captain, Ryan Davis (Bath Rugby), Matt Riley (Sale Sharks), Toby Flood (Newcastle Falcons), Ben Foden (Sale Sharks), Alex Rogers (NEC Harlequins), Chris Brooker (Bath Rugby), David Wilson (Newcastle Falcons), Richard Blaze (Worcester Warriors), Tom Croft (Leicester Tigers), Iain Grieve (Bristol Rugby), Michael Hills (Sale Sharks), James Haskell (London Wasps). Reps: Rob Webber (London Wasps), Tom Mercey (Saracens), Chris Robshaw (NEC Harlequins), Jordan Crane (Leeds Tykes), Danny Care (Leeds Tykes), Ryan Lamb (Gloucester), Anthony Allen (Gloucester)
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