The Dennis Dart SLF (Super Low Floor) marked the wholesale introduction of single-deck low floor buses in the United Kingdom in 1995, after many small-scale demonstrator usages. Low floor buses were rapidly introduced on high-profile routes, notably becoming a requirement for London Buses contracts. The Optare Solo introduced in 1997 marked another step change with inroads into smaller usages traditionally served by minibuses. The final phase came with low floor double-deckers the Dennis Trident 2 and Volvo B7TL entering the mass market, even though they were introduced after the Optare Spectra.