The British Rail Class 357 `` Electrostar '' alternating current ( AC ) electric multiple units ( EMU ) were built by ADtranz , Derby ( now owned by Bombardier Transportation ) from 1999 to 2002 at a cost of approximately Â # 350 million . The British Rail Class 357 `` Electrostar '' alternating current ( AC ) electric multiple units ( EMUs ) were built by ADtranz ( now owned by Bombardier Transportation ) at their Litchurch Lane Works in Derby , England , in two batches from 1999 to 2002 at a cost of approximately Â # 292 million .