Evanelpus
What about Duxford? The runway could be extended westwards, a whole new technical site built on the southern perimeter without affecting the IWM. The additional aircraft movements would be pretty minimal, the IWM would get some useful rent and the employees would not have to re-locate.
Sale of the existing aerodrome would offset the re-location costs for Marshalls and they might even be able to retain their design office/ management offices etc. on part of their present site.
Finally, the existing GA operators could possibly still survive a short move and private owners won't be left with nowhere to go.....
All in all, a no-brainer!!
MB