1) the runway at Cambridge is just under 2000m long, capable of handling empty B747s for maintenance, but only just on limits for the Ryanair & EZY fleet, both of whom demand a 2000m runway for their Ops.
2) Agreed that the airport is prime building land, but the south side of the airfield has very poor drainage and the local authority have already stated that it will never get approval for building land.
3) The only taxiway to the "Terminal" is entirely unsuitable for B737 and the like aircraft, it would have to be rebuilt at considerable cost to someone.
The "terminal" is very small, unable to meet with the demands of any high volume operation, and it too would require significant investment to expand, equip and staff it.
4) Major expenditure would have to take place on the approach road and car parking, as it stands, Cambridge is entirely unsuited to high volume passenger op's.
5) The board of Marshalls, as I understand it, have always resisted any "major commercial development" on the grounds that all the airport revenue is derived from maintenence and executive op's. Their thinking being that commercial ops come and go overnight, whereas maintenance and the executive op's are a more predictable source of revenue stream.
6) Marshall's would only ever move from Cambridge if whoever bought the airport paid their full relocation costs to elsewhere in addition to the price of the airport.
That's just about it - Marshall and Cambridge will remain together for the forseeable future.