A clumsy yet kind-hearted boy on the cusp of adulthood discovers heroism comes from within, during Manuel Sicilia's computer-animated adventure.

Justin And The Knights Of Valour is a stirring tale of derring-do set in an olde worlde kingdom steeped in myth and magic that was once ravaged by dragons.

A predominantly British voice cast adds lustre to the simplistic screenplay, co-written by Matthew Jacobs and Sicilia, including over-the-top comic turns from David Walliams as a demented wizard and Rupert Everett as a painfully vain evil henchman, who is a slave to sartorial daring.

The setting is reminiscent of the splendid 2010 animation How To Train Your Dragon but Sicilia's picture lacks that film's heart and soul, only faintly tugging our heartstrings when the ill-prepared hero fears all of his efforts have counted for nought and whimpers, "I wanted to come back a knight but I'm coming back a loser!"

A flame-throwing toothless crocodile is hurled merrily into the sweet and inoffensive mix as the narrative ambles at a gentle pace, building to the inevitable moment when fears are cast aside and gallantry struts forward to win the day.

The eponymous hero is Justin (voiced by Freddie Highmore), a sweet-natured boy who dreams of becoming a valiant knight like his grandfather, Sir Roland.

However, the Queen (Olivia Williams) has banished knights from her kingdom, and has placed her trust instead in lawyers including Justin's father Reginald (Alfred Molina), who wants him to abandon his dreams and pursue justice instead.

During a visit to his gran (Julie Walters), Justin in inspired to defy his father.

"If you want to be a knight, you'll need a quest," Gran tells him tenderly and Justin decides that he will bid farewell to his sweetheart Lara (Tamsin Egerton) in order to find his grandfather's sword. En route, he joins forces with a plucky barmaid called Talia (Saoirse Ronan) and a soothsayer called Malquiades (Walliams), and gains valuable training from three wise monks - Blucher (James Cosmo), Legantir (Charles Dance) and Braulio (Barry Humphries) - at the fabled Tower of Wisdom. Meanwhile, banished Sir Heraclio (Mark Strong) and his sidekick Sota (Everett) exploit the absence of the knights to plot a coup.

Justin And The Knights Of Valour lacks the visual sophistication of a lot of recent animations but does boast one stand-out sequence: a history lesson styled as a tapestry come to life.

Vocal performances are solid but there's a noticeable lack of sparkling one-liners and the grand finale lacks the big emotional wallop.

The underlying message of kindness and compassion, emphasized when one character declares "There is no honour in seizing power by force", isn't laid on too thick between some competently executed set pieces.