The question is not clear. where are you applying for a NIE?
What nationality are you? If Outside of EU then you need a visa.
If you lie on you application it means that things could end up pear-shaped. Put the address you live at and change it later when you have found a place to rent in Spain.

 

I live in UK currently and will apply myself at the Spanish consulate here. It says on the form "Address in Spain" so thought I needed an address there to use.

 

Anyone can get an NIE you don't need a Spanish address. Many non residents have them (we had ours years before we moved over and our UK address was on the paperwork).

You will have to give a reason why you want one. (or you used to when we did ours)...