Sognandoil380,
Don't worry about the national insurance number! This is something you would need to apply for through HM Revenue & Customs once you have been given employment.
A friend of mine, not British citizen, completed a temporary contract without the national insurance number. It's actually for you as to how much taxes you should pay.
At the interview, explain that you will apply for it should you be successful as you are not a citizen of the UK! This is what my friend did and it worked out well for him.