Sara Pascoe welcomes the four semi-finalists into the sewing room as they get to work with utilitarian clothing, with a place in the final at stake.Judges Patrick Grant and Esme Young challenge the sewers to make an office staple – the trench coat, which originated as part of a military uniform. They must tackle the multiple parts that make this coat so distinctive, from the storm flaps to the epaulettes to the double-breasted design.The sewers really need to use their imaginations in the Transformation Challenge as it turns to housework and making a garment from old cleaning products, including cleaning cloths, rubber gloves and mopheads.The Made-to-Measure Challenge is boiler suits. Once worn to stoke boilers, they are now a fixture on the catwalk and high street alike. Multiple pockets feature, but the sewers' biggest challenge is to make sure their boiler suits fit their models perfectly around the crotch and bottom.Who will get promoted to the final, and who will be pipped to the post and take their leave of the competition?