The British Rail Class 43 is the classification used for the InterCity 125 High Speed Train power cars, built by BREL from 1976 to 1982

The class are officially the fastest diesels in the world, with an absolute maximum of 148mph, and 125mph regular service speed (200 km/h)

InterCity 125 is a brand name used to describe two Class 43 power cars with a rake of Mark 3 carriages in between to form a complete train.

When originally built at Crewe Works, the InterCity 125 units were considered to be diesel multiple units, and were allocated Classes 253 and 254 for Western and Eastern Region services respectively

However, following both problems with the power cars and the operational ease of removing power cars to perform scheduled maintenace, unit formations were abandoned and from then on HSTs were considered to be formed of two locomotives with a rake of semi-permanently formed Mark 3 carriages in between

The 197 power cars produced are numbered 43002-43198. 43001 was applied to one of the two prototype power cars, while the first of the pair, now preserved, became 43000, an unusual number as no other loco carried a triple-0 number

Introduced between 1976 and 1982, at a time when the maximum speed of British trains was limited to 100 mph (160 km/h). The increased speed and its rapid acceleration and deceleration made it ideal for passenger use, which slashed journey times around the country. The prototype InterCity 125 (power cars 43000 and 43001) held the world record for diesel traction at 230 km/h in 1973 and at 238 km/h in 1987

In the Western region, InterCity 125 trains designated Class 253 were introduced initially for all services from London to Bristol and South Wales, and then extended for most day-time services from London to Devon and Cornwall

The Class 47 locomotives still operated the cross country services from Cornwall and South Wales to the Northeast via the West Coast Main Line, as well as London to the Midlands/Welsh Marches. However, Class 43's also replaced these services once the third batch of power cars were delivered. All of these formations are formed in a 2+7 formation, normally with two first class carriages, a buffett and four second class carriages sandwiched between two power cars

On the East Coast Main Line, the InterCity 125 designated Class 254 was the staple stock from the retirement of theDeltic locomotives in 1980-82, to the introduction of the Intercity 225 following electrification in 1990

During 1987, eight power cars were converted for use as Driving Vehicles with Class 91 locomotives during trials on the East Coast Main Line. The power cars were fitted with Time Division Multiplex equipment that allow them to directly control a Class 91, buffers and were moved over to the ECML for and were used on workings with Class 89 and then 91 locomotives from London to Leeds. After the Mk4 stock had been delivered, the power cars had the TDM equipment removed, and then reverted back to their normal duties. The power cars which were used for this project can be easily identified as they are still fitted with buffers

Class 43 formations are still used today on Hull, Edinburgh and north of Edinburgh services (ie - where electrification has still not yet reached). The basic Eastcoast formation is a 2+8 formation, normally with two first class carriages, two buffetts (one at the end of the first class section, one in the middle of the second class section) and four second class carriages sandwiched between two power cars.

In 2004, 196 Class 43 locomotives were passed to three private companies:

• First Great Western - the former Western Regional services from London
• Great North Eastern Railway - the remaining London based services which were not accessible under the electrification program
• Virgin Trains - the Cross Country services from Devon and Cornwall to the Northeast and Northwest

Virgin quickly refurbished and supplemented their fleet as they replaced the Class47's, and then shortened the formations to make them quicker. This released units, which were quickly picked up by Midland Mainline

In conjunction with the WCML Line Upgrade, Midland Mainline were asked by the then-SRA to operate London-Manchester services via the Midland Mainline and the Hope Valley into London Marylebone station. In an operation dubbed "Project Rio", a large percentage of the stored VXC powercars were overhauled and returned to service in an enlarged Midland Mainline fleet

The first operator to dispense with using HST sets was Virgin Trains on both the CrossCountry and West Coast franchises in the period 2002-2004 following replacement by Voyager high speed DEMU's and the commencement of the CrossCountry Operation Princess timetable. The majority of the former Virgin Cross Country fleet went into storage with a small number moving straight to Midland Mainline to supplement its fleet, suffering reliability problems at the time.

Ending on 10 September 2004, the Project Rio fleet was gradually disbanded with powercars moving to First Great Western, GNER or into storage. Following withdrawal by Virgin in 2003, several power cars are now in store, locations including Minehead at the western end of the West Somerset Railway

Four of the batch of 197 power cars have been written off and scrapped:

• 43001 - after prototype testing and approval, both it and its sister were transfered to departmental duties. 43000 is now preserved at York Railway museum, while 43001 was cut up by Booth Roe at Rotherham in December 1990
• 43173 - written off in the Southall crash of 19 September 1997 and disposed of once the enquiry had been completed
• 43011 - demolished in the Ladbroke Grove tragedy in 1999, being disposed of immediately after completion of the enquiry into the accident
• 43019 - written off in 2004 after colliding with a car parked on a level crossing at Ufton Nervet between Reading and Newbury. Powercar 43139 is dedicated to the driver Stanley Martin, 54, of Torquay, Devon who, sadly, perished in the tragedy

The Class 43, having been operation since the late 1970s, is due for replacement by ‘HST 2’. The development cycle for the replacement series is such that the existing fleet may be required to operate through to 2015 or beyond. In support of this, a life extension program is being considered. Such a programme will require ROSCOs and TOCs to address a number of issues within the power cars.

During the late 1990s a batch of 25 HST power cars were re-engined utilising 12VP185L traction engines. These new Paxman engines attempted to bring improved fuel consumption and reduced emissions to the HST. However they have proved to be less reliable in service than hoped. The 12VP185L has also been introduced fleet wide within the Australian XPT series

During 2005, two Class 43 locomotives (43004 and 43009) operated by First Great Western were fitted with new MTU 16V 4000 engines. These two vehicles are currently being tested in passenger use on the Great Western Main Line. They can be identified by their modified headlight clusters, the quietness of the engine and the new Neon Livery. Also within First Great Western two power cars (43170 and 43179) have been installed with updated 12VP185L engines. Both engine combinations offer improvements over the existing Paxman 12RP200 'Valenta' engines, with reduced smoke and exhaust emissions.

GNER has obligations following its re-franchise to replace engines within its Class 43 fleet, and is pursuing the MTU engine option following the trials conducted by First Great Western. First Great Western particularly compared the performance of the MTU-engined units with modified VP185 units.

In December 2005, First announced that all Great Western power cars will receive the MTU engine. The first batch were sent to Brush Traction for the installation of the new engines. The GNER fleet will also be fitted with MTU engines alongside the Great Western programme

The youngest of the power cars is now 25 years old and thoughts are firmly set on the replacement for the High Speed Train. The project, known as HST2, is being spearheaded by the Department for Transport along with First Great Western and GNER. It is "back on track" following a period of uncertainty during the reign of the now abolished Strategic Rail Authority

In the Railway Series, there are two diesels who had the same type as the Class 43 (HST). They were Pip & Emma.

• InterCity 125 - Two Class 43 power cars sandwiching a rake of Mark 3 coaching stock.

• Mark 3 coaching stock - Sandwiched between two Class 43 power cars to form an InterCity 125 set.

• High Speed Train - History of High Speed rail transport in the UK in general.

• InterCity - General InterCity brand before privatisation of British Rail.

• XPT - Australian high speed train whose design was derived from the Class 43

Wikimedia Commons has media related to British Rail Class 43.