I'm guessing you'll have to provide the same types of information that folks often have to show to employers, GP receptionists, etc -
Copies of visas and print-outs from the UKBA website that say "Whilst you're application is being decided you are legal per your last visa" - etc
I do suspect they'll be folks with difficulties (mostly those who move on student visas-work visas without a British spouse) with landlords not knowing the laws and rights to live, etc and will cause some headaches -afterall, landlords won't know if you're forging a visa document or not. There will probably have to be a UKBA helpline or something.
Yeap, only going to make things harder. Wonder what my landlord will think?