It's a grey area. As far as I understand, there is nothing in the UK ANO that explicitly states such an approach is illegal for UK/JAR licence holders. However, if you make such an approach you will not hear of potential hazards (such as cranes, tethered balloons etc) through the NOTAM system. Furthermore if you do screw up and someone gets hurt you won't have a leg to stand on.
I agree with SAS; fine on a good day but very dangerous if used in anger
Al