This very nice OO gauge locomotive by Heljan is 26521 a Class 26/0 diesel locomotive in Dutch engineers yellow and grey livery and running number 26 003. 

The British Rail Class 26 diesel locomotives, also known as the BRCW Type 2, were built by the Birmingham Railway Carriage and Wagon Company (BRCW) at Smethwick in 1958–59. Forty seven examples were built, and the last were withdrawn from service in 1994. Like their higher-powered sisters, the BRCW Classes 27 and 33, they had all-steel bodies and cab ends with fibreglass cab roofs.

The Pilot Scheme batch of twenty locomotives (D5300-5319, Class 26/0) were delivered to Hornsey TMD (Traction Maintenance Depot) on the Eastern Region of British Railways between July 1958 and March 1959. They were used on a variety of duties, notably including London commuter services into King's Cross station. 

By the middle of 1960, evaluation of the various Type 2 designs was complete and it was decided to concentrate all of the Class 26s in Scotland. As a result, the Class 26/0s were transferred to Haymarket, displacing the Class 26/1s to Inverness. Although some transferring of individual locomotives between the two depots occurred, the type was then allocated entirely to Haymarket and Inverness until 1987, apart from the brief allocation of a few locomotives to Kittybrewster TMD and Dundee TMD during 1960.

Like other Scottish Region Type 2s, Class 26 could be found on a wide variety of duties during the 1960s and '70s. 

Most were withdrawn by 1993, but some survived in preservation including 26 010 which remains in operational condition. 

The loco is in very good condition as you can see in the pictures, it is tested and runs. The lights may need a bit of attention. A complete external visual inspection has shown the overall condition is very good. It comes complete with its box. The box is in good if slightly shelf worn condition. 

Overall this is a really nice scale locomotive and would look fantastic on a layout.

Do please have a look at my other listings, I typically have various HO and OO locos on offer as well as an extensive range of imported N gauge locos and other items. 

Note: I do recommend all locos are cleaned & serviced, as they have some age to them even if the quality looks at the highest level (fairly standard advice for all locos!).