http://www.epolitix.com/1832-blog/blog-post/newsarticle/lords-reassured-over-spontaneous-dancing/

John King comments:
There is a serious point to the question of spontaneous dancing. Under previous legislation there were prosecutions for unlicensed dancing. In 2002, Westminster council successfully prosecuted Wolverhampton and Dudley Breweries because licensing officers witnessed the 'rhythmic moving' of customers to music.

Although not mentioned in the words of the Act, The S182 Guidance does detail spontaneous music and does regard this as being exempt.