In reply to alasdair19:
Hi. Portishead Quarry itself is large, but the bit where many climbers go - High Slab - is relatively narrow and doesn't contain a lot of routes. You can certainly walk to the top and abseil to bolts to set up, but don't expect to "reserve" those routes with in situ ropes for very long if other climbers turn up, especially at weekends. If it were me, I'd head for somewhere less popular and with a larger selection of shorter routes.