Generally speaking, I am against major changes (e.g. tax laws etc.) in the constitution. I don't think we should leave the Union, just be cautious about our involvement and make sure we don't go down the road of a United States of Europe.
Anyhoo, you shouldn't worry; those nice people in the government assured us it was just a, "tidying up exercise" (hmmm....)
its high time we stopped pretending that we havent already got one, 1972 we officially joined, 31 years and english people still think we're not part of europe. our unwritten uk constitution is so flexible that the as yet unwritten european constitution is already woven through it. to put it down on paper would formalise it, but in practice its already there.