If you work out the duty hours for 5/7 compared to providing 7/7 (365) even with limited opening the number of ATCOs required is significant.
It is sensible to start off gently and see how the service develops over the next 12 months.
The real issue will be the winter months, and a low Cumbrian cloud base from time to time using a NPA.
A Siberian high in the winter months would be ideal.