'ATC constraints' at Carlisle are due to a drastic shortage of suitably rated and experienced ATCOs. Everybody wants controllers with ADV/ADI and APS ratings nowadays, very few units have APP only.
Some airports will tempt inexperienced controllers by saying 'get the MER, then we will take you on and sponsor you for an APS rating'.
Safeskys in particular have suffered from this at Wycombe.