I understand they are SC-7 Series 3s which have a service ceiling of 22,500' but no side doors, but that Summit's third aircraft used is a Do 228 which has side doors, a service ceiling of 25,000' but both only have room for 19 pax never mind fully kittted paras.
Obviously been keeping my eyes on the A34 & M40 on my infrequent journeys past WotG.
Definitely looks like a (very) preferred bidder situation IMO but I may be wrong. (The also have Avro RJs, ATR-72s and DHC-8s)