People have different dates as to when the state came into being so I suppose it depends on what criteria they use. The Scottish monarch James VI inherited the English throne on the death of Elizabeth I of England in 1603. Wales at that time was politically regarded as part of the English kingdom itself and the English monarchs through conquest were already monarchs of Ireland too. However Scotland, England and Ireland remained separate (ie kingdoms) states. The Act of union between Scotland and England in 1707 wound up both those kingdoms and did actually create a new united kingdom of Great Britain. This was more commonly called simply 'Great Britain' though it could be claimed the UK dates from this time and that the 1801 union with Ireland was simply an extension of the borders just as the US has expanded since it was created!Others will say the UK proper was created in 1801 though it was of course reduced in the 20thC. I'm not sure which one to plump for!