I didn't think they were still in service Kev.
They aren't regularly. However recently privately owned heritage locos with mainline certificates have been hired in by freight operators. One of the Deltics (Class 55) was used recently by GBRf, and obviously now they're moved on to Westerns!
Here's an article about the Deltic in use: http://www.railwaystoday.com …gbrf-hire-rumours-latest/