In reply to rob malik:
Capel Curig Pinnacles; Little Tryfan. Both provide everything you need for practicing basic rockclimbing belaying techniques. The first is probably a better place to teach serious belay techniques, the second better for general rope-work, multi-pitch procedures (i.e real climbing and doing it safely).
But you're talking about scrambling, yet needing to 'practice', even though you say you are competent, which is very odd. The only way you can practice scrambling is by scrambling, and for that you don't need any ropes or harnesses at all.