Is this usual
Yep. Was for me on my Sherpa Mk2. The skewer ends (for a Shimano q/r, or the ends of a SON bolt-on skewer) fit inside the perimeter of the Thorn rack. This was also the case on some other bikes when I used Blackburn Low-Riders.
or have I missed a trick hear?
Depending on how the rack has been fitted and the presence of any spacers and the particular q/r or hex key skewer fitted, it is sometimes possible to gently ease the rack apart just enough to clear.
I found it much less hassle to simply remove the skewer. On my frame, running 2.0 Schwalbe Duremes, I needed to deflate the tire partially to ease it past the brake pads anyway.
My Mk2 had no "lawyer lips" on its fork dropout. If you have the later Mk3 or another Thorn equipped with them, you'll need to loosen the skewer a few turns to get it past those anyway.
Business as usual.
All the best,
Dan.