the purpose of satisfying the diverse needs of this requirement; it was noted that the envisioned modifications would necessitate a significant reduction in the number of seats available. All were to be withdrawn by December 2019. Northern ordered the Class 195 and Class 331 units to replace the Pacers, as well as taking on spare stock from other operators. However, due to the late delivery of the new trains, the 144s were to remain in service in the South Yorkshire area until the middle of 2020. Northern accordingly sought and received a dispensation allowing continued use until 31 August 2020, on certain specified routes only. Withdrawal Following the outbreak of COVID-19 in the UK in March 2020 and the resulting curtailment of passenger services, Northern withdrew the entire fleet prematurely and by mid-April had placed all 23 units in storage; 18 units at the Keighley and Worth Valley Railway and the remaining five at Heaton Traction Maintenance Depot in Newcastle upon Tyne. Three units were subsequently scrapped, while the other 20 were distributed to preservation groups and other non-railway users. Class 144e The Class 144 Evolution (or 144e) proposal was publicised by fleet owner Porterbrook in 2015, as a way of bringing the fleet into compliance with the PRM-TSI requirements and thus extending its life past the compliance deadline at the end of 2019. One unit, number 144012, was refurbished to the Evolution standard and displayed as a proof-of-concept of upgrades including; installation of a universally-accessible toilet, provision of two wheelchair spaces, provision of a luggage rack and space for two bicycles, installation of new Fainsa seats, installation of passenger WiFi, installation of passenger information displays and automatic voice announcements, installation of CCTV in the saloon, along with forward-facing cameras in the cabs, and, conversion of internal lighting from fluorescent to LED. Porterbrook stated that it had paid £800,000 to prepare the demonstrator unit, but claimed that a price of £175,000 per vehicle could be achieved in volume production. It was planned that the demonstrator would enter public service in April 2015, but this was delayed until later in the year. Following withdrawal it was sold in 2021 to Network Rail, but later scrapped. Incidents A Northern Rail 3-car Class 144 unit caught fire near in Rochdale on 21 November 2013. Fleet details A total of 23 Class 144 units were built. The first thirteen of the classnumbers 144001 to