Alexander ALX400

Overview
The Alexander ALX400 is a bus body found on B7TLs, Tridents and DAF DB250s. It was a very successful body that was later replaced with the Enviro400 body.
The ALX400 body was manufactured in Northern Ireland at the Alexander Dennis bodywork manufactures (then known as 'Alexander') from around 1998-2006. The ALX400s production was at its peak in the year 2000 with around 800 or more built however, production slowed down after 2001. A few more were built up until 2006 where production finally ceased.
The majority of Alexander ALX400 buses were finalised with Dennis Trident chassis, the second most popular chassis for the body at the time was the was the Volvo B7TL chassis, and the least popular being the DAF DB250 chassis (later known as VDL).
The Alexander ALX400s were some of the first low-floor double-decker buses to be introduced to many companies (known as 'Elite' standard with FirstGroup) as well as some of the first buses with significant buggy and wheelchair space.
Most ALX400s built had ZF Ecomat gearboxes added later, but a good number of them were given the latest Voith gearboxes (note: no larger buses were given Allison gearboxes).
Distribution
The majority of ALX400s were purchased by Stagecoach from 1999-2006 with around 700+ buses bought in total. The majority of the these buses had the Dennis Trident or Trident 2 chassis; only a rare few had Volvo B7TL chassis. The Trident 2s have a newer interior compared to the original ones which are now withdrawn. Many ALX400s were shared out with other depots across the years meaning almost all Stagecoach depot featured ALX400s at one point.
FirstGroup were the second biggest consumers. Around 85 buses were bought for First West Yorkshire in 2000 following on with about another 50 in 2001, but significant decline in 2002 with only a handful of others bought with slightly upgraded interiors. First South Yorkshire bought some more in 2003 however. A large number of middle-door ALX400s were bought by First London in 2002 which were later transferred out to other First divisions. The majority of ALX400s bought by First had Volvo B7TL chassis, but a rare few around Devon and Cornwall depots had Dennis Trident chassis (as well as a few Glasgow examples).
Arriva bought around 250 ALX400s for their fleets as well from year 2000+. The most popular chassis for most of these was the DAF DB250 which was a very popular chassis for Arriva at the time with many buses featuring them until around 2006 where they focused on the SB200. A few ALX400s with Volvo B7TL chassis were bought for Arriva Yorkshire in 2000 and a few other Dennis Trident ones for more southern counties. Arriva Yorkshire stopped purchasing ALX400-bodied vehicles in 2003-2004. 
A few other companies purchased ALX400s with a mix of the three chassis types available for the bodywork like Travel West Midlands and Dublin Bus in the Republic of Ireland with a mixture of Dennis Trident and Volvo B7TL chassis.