Should the United Kingdom approve the treaty establishing a constitution for the European Union?
Nosemonkey edit: For those who think this sounds a tad familiar, the wording was originally set at the start of December (although the article linked in that post is now behind a subscription wall). It is now, however, as final as these things get. You'll also notice that it cunningly leaves room for future maneuverings should this particular constitution prove not up to scratch, as it's only "the treaty" which is to be approved, not necessarily the constitution itself, which in any case is referred to only as "a" constitution... Not quite as dodgy as the 1975 referendum, but no doubt the more hardened Eurosceptics among you can find some ammunition here.
By the way, here's a summary of what changes the constitution will bring, and a quick look by Martin Stabe at a major problem with the referendum which today's bill should be addressing.