The YCA Halibut was a prototype airbraked ballast wagon, though after a short period of testing it was relegated to being used as a general purpose spoil wagon. The wagon (No. DB981000) was introduced in the early 1980s (probably '82) and continued in service until at least 1999, though there have been sitings post 2000. The wagon spent a lot of time on the Southern Region though it often ventured to other regions, especially after privatisation.
This wagon is designed to sit on N Gauge Society Y25 Fabricated Bogies and should be painted in the "Dutch" livery.
Photographs of the real thing can be see on Paul Bartlett's excellent website: http://paulbartlett.zenfolio.com/halibut