The majority of Middlesborough to Hexham services are worked by 142s, and there are also a good number of 142 diagrams on the Darlo to Saltburn turns. The Whitby services are, as MattE2010 says, all usually worked by 156s though.When I was in the Middlesborough area the other week, every Northern unit I saw was a 142, including the 1500 to Nunthorpe. I didn't get to see the Whitby train though (Northern wouldn't hold it after cancelling the connecting train from Saltburn).
They may have done in the past but I doubt Darlington and Middlesbrough crews sign 150s. All Whitby services are 156s now, although 142s get as far as Nunthorpe. I did have a 142 all the way from Newcastle to Whitby and back on a summer Sunday a few years back.Do 150s ever make it to Whitby?