According to the Commission in 2005 the EU adopted 1,691 regulations, directives and decisions. According to the Office of Public Service information, in 2005 Britain enacted 3,326 statutory instruments (secondary legislation via which all EU legislation is adopted) and according to Wikipedia just 23 acts of primary legislation were passed (those quaint acts of Parliament that we used to be governed by).
As a matter of straight arithmetic therefore the EU is responsible for fully 50% of the total enacted law of the UK in 2005. This flatters the domestic contribution since a great proportion of domestic statutory instruments deal with the alteration of the status of individual schools hospitals etc. and is therefore not law binding on the land as are all EU directives.
Since 1965 fully 22,000 individual acts of enforceable law have been promulgated by the the EU and passed into British law via secondary legislation. In that time the British Parliament has passed just 2355 Acts of Parliament. In other words British primary legislation (the kind that's debated and modified by our elected representatives) comprises an average of 10% of the law passed in Europe over a forty year period. In 2005 the figure was 1%.