Wear comfortable, loose clothing. Yoga pants, jogging bottoms and long sleeved T-shirt or rugby/football kit. Several layers for you upper body would be a good idea - it may be cold to start with, but you should get quite warm during the class.
If you have mats and blocks - please bring them. Otherwise I can provide some sets for a small fee (£1 per session to cover their cost) - please let me know in advance if you need them!