After paying a tidy sum for a UK visa, why shouldn't they be given priority
As someone who worked in various visa sections around the world I can assure you that the British Govt make a whacking loss on visa operations. I would argue that as a taxpayer I am entitled to have as many UKBA staff on duty to deal with UK nationals returning to the UK. If that means a visa national has to queue for longer, so be it. When I visit foreign countries I am not afforded better treatment at immigration control than those holding passports for the country I am entering.
Will anyone behind the desk understand (or even care)
Yes, immigration officers do have a brain (although sometimes a minority don't show it occasionally) and can tell the difference.