Buccsociety,
I know it does not directly answer your Downbird question, but another company that could help is Hutchinson Engineering Services, Weston Nr Newark [tel: 01636 821648].
They have moved various items for Newark [Sea Harrier, Bulldog, Viggen]; Sea Harrier for Midland and various other Sea Harriers for a company off A1 south of Grantham.
From published pictures of Newark’s Viggen move Hutchinson seem to have their own escort vehicles, which may help with your wide-load permissions.