The registrar probably isn't just being difficult. S/he just isn't allowed to have individuals with visas give notice there, most likely.
You have to go to one of the "designated" register offices since you're subject to immigration control. You can find a list of them here:
ClickyYou just have to give them proof that you've been living at your current address for the required period of time, and of course take your passport with your visa. For instance, we went to Nottingham to register (we live in Derby, but Derby's register office isnt a designated one). We just phoned them up, made an appointment, and then took in our electric bill and council tax statement (I wasn't sure if we'd need separate proof of address, so we just took both). The lady there interviewed us separately, then we paid our £60 and she mailed off something to Pershore (which is where we're getting married). About two weeks later I went back to Nottingham to collect our authorities, and then I sent them off to Pershore. It's easy, I promise.