500'
...... or as your height dictates!
My instructor did mention that some students only manage low level circuits on their precautionary landing lesson as controlled aerodromes are sometimes reluctant to let you do them. We were lucky this week in that we were the only ones around, and even then we had to join crosswind for another runway before being given permission from ATC to carry out 3 touch and go's.
Worth doing. Feel it was a very valuable lesson.