> The United Kingdom consulted its citizens directly only after joining the European Communities: following the British general election of October 1974, the Labour government of Harold Wilson held a referendum to fulfill one of its campaign promises. The non-binding referendum was held on 5 June 1975, some two and half years after the UK's accession. It was the first ever national referendum to be held in the UK, and the "yes" vote won by a landslide 67.23% on a 65% turnout with 66 out of the 68 local counting areas returning majority "yes" votes.

I'm inclined to count that.

Agreed, it is pooling sovereignty. The UK already does that with a union of England, Scotland, Wales and Northern Ireland. Pooling sovereignty is often regarded as a benefit on the whole.