A recurring theme across the UK on unelectrified lines is that it is not possible to provide enough trains to satisfy or stimulate demand. This is not down to austerity but is a consequence of the Government plans switching from minimal further electrification to a rolling programme of electrification that will go over the lengths and breadths of the British rail network. Up until 2008 or so the Labour government had not seen the rail network in the same way as it is seen now - they preferred to make do and mend with what they had, replacing things that needed replacing but not doing anything particularly radical. This extended to a belief that the best option for the rail network was to depend upon bio-diesel to power trains, as electrification was seen as another complicated system to cost money and go wrong, to the point that the Government were willing to buy brand new high speed diesel trains for the unelectrified Great Western Main Line.
This began to change, starting with Crossrail and then moving on to founding of HS2 Ltd and the announcement of the rolling programme of electrification - partly in response to the state-owned rail infrastructure owner/operator Network Rail pointing out that it would be cheaper in the long term to electrify the GWML than it would be to buy new diesel trains for it. At the same time a proposed plan to order 200 diesel multiple unit carriages was cancelled, and the plans for future electrification has made the economics of buying new diesel trains unworkable, even before considering the fact that the EU emissions regulations changed to prevent a continued manufacturing run of existing designs. The only way to provide extra diesel trains for routes is to electrify other ones to free up their diesels, or to build bi-mode trains that are capable of running on both diesel and overhead wires and would have a full economic life ahead of them. In the case of the Fife Circle line, the Scottish Government (through Transport Scotland, who are mostly responsible for the planning of Network Rail and the ScotRail franchise in Scotland) are funding the electrification of other lines throughout the Central Belt of Scotland at the moment and the diesels freed up from these lines will be available to replace the loco-hauled rakes, and to run the new Borders Railway down to Tweedbank.
To complicate matters even more there is a looming deadline of 2020 to make every train in the UK fully compliant with the EU's Technical Standards for Interoperability - Persons of Reduced Mobility requirements. At the time this deadline was put in place, back in the early 1990s, it had been assumed that the last fleet of non-compliant DMUs to be introduced would have been retired before this deadline. As passenger numbers and the number of diesel trains needed have grown without the ability to order more, the possibility of this deadline being met is now particularly slim. To make matters even worse, the Pacer class of train, which consists of a bus body on top of a freight carriage, have more than passed their design life and are thoroughly unsuitable for the modern railway. These trains are found on what tend to be uneconomic lines in the North and South West of England and in South Wales.
