In 1986, the route came under control of the "Thameslink" subsector of newly created Network SouthEast. From 1987, new dual-voltage Class 319 units were introduced on the route, allowing the creation of a new cross-London service, from Bedford to Brighton, via Farringdon and City Thameslink station. The Class 317 units were displaced to outer-suburban services on the WCML out of London Euston to Milton Keynes and Northampton. They replaced the slam-door Class 310 units, which subsequently transferred to the London, Tilbury and Southend railway.