Actors Sid Owen and Tina Malone, champion Paralympic swimmer Liz Johnson, BBC Breakfast presenter Louise Minchin and TV personality Amy Childs take part in the third heat.In the Mystery Box challenge, they must create a dish using ingredients based on an American diner theme. They are then thrown in at the deep end as they take part in lunchtime service at two busy London restaurants, cooking for the public.Then it is back to HQ as the contestants prepare a two-course meal to convince the judges they deserve to retain their place in the competition.

This week's heat continues with the four celebrities battling for a semi-final place.The first challenge involves two contesants teaming up to create a main course and pudding. However, one takes over the work of the other without any verbal communication, before the two come together at the final stage.Following that, still paired up, they must prepare lunch for over a hundred staff at Vigin Atlantic's training centre, making meat and vegetarian dishes plus dessert in high volume.Finally, back at HQ, the chefs cook a two-course meal to be judged not only by Greg and John, but the reigning competition champion as well as two previous finalists.

The hunt for a champion continues as we welcome the final five celebrities to the challenge in the last of the heats. Trying to impress judges John Torode and Gregg Wallace are Olympic champion boxer Audley Harrison, Strictly Come Dancing professional Gleb Savchenko, antiques expert David Harper, TV presenter Cherry Healey and singer and entertainer Jimmy Osmond.The first challenge for the five hopefuls is the Invention Test, the infamous test of imagination and creativity. This episode's box has a French theme, and the celebrities must use the given ingredients, including duck, bacon, Morteau sausage, cheese and pears, as well as a larder, to create just one dish - sweet or savoury. With nerves running high and just 60 minutes to create something from scratch, the celebrities must think on their feet to impress the judges.With the first test over, there's no let-up as the celebrities face paying customers for the first time, working during lunchtime service in two busy London restaurants. Audley, Jimmy and Cherry are sent to Kojawan, where they face a real baptism of fire trying to keep up with orders in this busy Pan Asian restaurant, while Gleb and David try to impress and master the dishes at Indigo.In the final test of culinary creativity it's back to the MasterChef headquarters, as the contestants are asked to prepare a two-course menu of their own design. The celebrities work furiously in a last attempt to prove themselves to the judges, because at the end of this test one of them will be going home.