The week's best chefs return for the first quarter-final, and this is where the battle really begins. Their first challenge is the Invention Test - but this one has a twist. The quarter-finalists must create an exceptional plate of food from trimmings. Gone are the arrays of quality ingredients they are used to cooking with, instead the judges ask them to make their dishes from kitchen scraps, including bones and offcuts, fish skins, over ripe fruits and cheese and stale bread.

Failure to impress will cost them. After judging their dishes, Marcus and Monica decide who can continue in the competition and who must go home.

The remaining contestants then tackle their most nerve-racking test to date when they face the scrutiny of three of the UK's toughest restaurant critics to prove they are worthy of a semi-final place.

The chefs have one hour and 15 minutes to create a jaw-dropping two-course menu to impress the daunting panel - Charles Campion, Tracey MacLeod and Jay Rayner.

Only the most exceptional chefs can make it through to the semi-finals and stand a chance of becoming 2014's Professional MasterChef. Show less