Crystal Holidays
They often use other operators for their Lakes & Mountain program, its only one flight a week (and an odd day at that) so using a based operator is probably cheaper than the positioning cost before and after. Its unlikely that you will be able to buy a seat on it through Jet2, you never could when the this was done by bmi on the ERJ, bmi tended to use the ERJ when they would otherwise have been parked up at weekends, nowadays they tend to cover mainline thin routes at weekends.