 The station's Controller of Drama approved of the idea and had the crossover commissioned, spearheaded by "Casualty" executive producer Mervyn Watson, and "Holby City" Tony McHale.The writer and producer for the first, two-part crossover were selected from the "Holby City" crew.Logistical difficulties arose from the fact the two series are usually produced 120 miles apart, with "Casualty" based in Bristol and "Holby City" in Elstree.