Brompton's bicycle factory in West London is the largest in Britain, producing 150 of its distinctive folding bicycles every 24 hours.

In the fourth episode of Inside the Factory Gregg joins a multi-stage manual production line to make his very own bike. He'll learn how to put together 1200 individual parts. He'll also attempt to braze a bike frame together using extreme heat of a thousand degrees, a skill that takes years to master. He'll visit a leather saddle maker in Birmingham that's been making saddles for 150 years and discover how they use cowhide from UK and Ireland cows because the cold weather means they have thicker skins.

Meanwhile, Cherry Healey gets some tips from Cycling Team GB to help us all improve our pedal power. She also learns how to paint a bike frame fit for the British weather using an electro-static charge and a 180 degree hot oven. Cherry also investigates why cyclists and trucks are such a deadly combination: in London alone there have been 66 fatalities since 2011 and half of them were collisions with a truck.

And historian Ruth Goodman reveals that folding bikes date back to the 1870's, and how 70,000 folding 'parabikes' were manufactured during World War II, some of which played a role in the D-Day landings. She'll also find out how the invention of the safety bicycle in the late 1880's was used by Suffragettes to ride to rallies and spread the word in their fight for equality.

Gregg Wallace joins a human production line in the largest sports shoe factory in the UK to see how they produce 3,500 pairs of trainers every 24 hours by sewing 32 million individual stitches and using 140 miles of thread. He makes his own pair of shoes and discovers how they put together 27 different pieces made from eight different materials which require auto- and manual stitching, and finishing with a 'roughening' robot and a hot oven. He also meets the man who comes up with new designs, including trainers inspired by the three most popular pub names in England.

Meanwhile, Cherry Healey gets hands-on in a tannery to help them process thousands of rawhides into finished leather for the nation's shoes, and finds out how a ballet shoe company painstakingly turns 37,000 square meters of satin into a quarter-of-a-million ballet shoes - some of which only last for one performance. She also gets to design her own court shoes at Cordwainers College in London, where she learns how to turn creative ideas into commercial products - last year, sales of women's designer shoes topped £532 million.

And historian Ruth Goodman reveals how, when the sewing machine was first introduced into shoe factories in the mid-19th century, traditional shoemakers went on strike, rebelling against joining a restrictive production line. She also traces the surprising origins of the humble trainer to the back streets of Bolton, where Joe Foster invented his running spike in 1895, above his father's sweet shop, and discovers that Reebok trainers were originally British.