from the site :

"The exhibition runs from 21 February to 29 March 2007. It is open from 8.30am – 4pm and although the exhibition itself is free there is an entry charge of £9.50 to the Cathedral – concessions £8.50"

so how does that make the exhibition free? Theres an admission charge, albeit to the cathedral, but as the exhibition is within the cathedral it cannot state that its free. If you turn up and say "im just here for the exhibition" and they let you in, then fair enough but somehow I can't see that happening.