The Big Performance tour bus hits London and Gareth is testing his group of under-confident children like never before, as he asks them to write their own song to perform later that day.

So where better to get them in the mood than the BRIT School - a place of excellence for nurturing young talent. The list of alumni reads like a who's who of the biggest names in pop - Adele, Jessie J, Leona Lewis and the Rizzle Kicks all studied here - and now Gareth's newest singers are being inspired by their surroundings.

To get his group writing a meaningful song of their own, Gareth suggests drawing on their personal experiences and it does not take long for a common theme to arise - being bullied. With the help of a songwriter who has worked with Will Young and Eliza Doolittle, can the group turn their ideas into a real song? By focusing on feelings they have all shared, Gareth hopes their spirit will inspire others, because their final performance will reach thousands as they will be singing live on BBC London radio.

Local lad Taylor has his own concerns about singing to London listeners, as he has been teased in the past for his love of singing and he has started to believe what he has been told - that singing high notes is girly. So Gareth has a struggle on his hands to convince Taylor to just go for it.

To help prepare for such a major performance, the group are joined on the bus by a special celebrity guest mentor, who knows a thing or two about singing for thousands of people - former Spice Girl Melanie C. With her tips on staying cool under pressure, can the group do their song justice to thousands of listeners, or will it be a step too far? Show less