Fairford is a long way from St Ives! (over 200 miles)
More likely they use NQY and bring a lot of security, or bring him over in something smaller (eg, 757, like Trump at SOU) that could use the Military security of Culdrose (longest runway 1800m)
which is pretty close.
NQY has a lot of space, plenty for the Govt widebodies and military accompanyment.