Pretty much all the trunk flying is with Jet 2 & Titan but there are still some turbo prop operations linking in the outlying areas in Scotland & the islands (JER/GCI/IOM)
If I recall correctly, the Channel Islands link in to the Postal Air Network at BOH, IOM links in to EMA. It therefore would seem logical to link IOS in via EXT. No point moving it by road & I very much doubt there would be sufficient mail to make a NQY flight worthwhile.