Be prepared to be told you can't do it that way as well. When I applied for my provisional, I had my photographs signed by someone who had known me for more than 3 years (a UK citizen), as requested. However, my application was sent back and I was told I had to go to a DVLA office to have my photographs verified, as I had not lived in the country for at least 3 years (or whatever the time requirement was). Nowhere on the forms did it say that was the requirement, but supposedly it was. So although it may seem like everything's been done according to their requirements, you might find out later that they won't go along with it.
It's all very random too...as I think there was at least one person on here who had no problem with their photographs.