In reply to Cheese Monkey:
The guidebook suggests that Coastguard Wall - ie the whole cliff - is 60m high; the database seems to confirm this by recording routes that start at the bottom as being in the region of 60m long, and an earlier guidebook gives Nazgul a length of 190 feet. Only one of the three routes mentioned (but not described) in South West Climbs vol 2 - Complicated Simon - actually starts at the base of the wall; the other two start higher up in the wall's right-side defining gully, just below the small gearing-up spot between boulders where the approach path arrives from the right. One assumes that Complicated Simon and the database's Coastguard Cutter are in fact the same route, although the latter is recorded (at 49m) as having the same length as Coastguard Slab - which obviously can't be quite right as the one route starts rather higher than the other and they both finish at the same level. One could, however, start Complicated Simon/Coastguard Cutter by traversing in from the higher location as on Severance - which wouldn't really involve missing anything as the initial section up to the vegetated clump is very easy; perhaps the database pitch length assumes this. So while in theory this route would seem to require a 60m rope, the various options of using the higher start, splitting the pitch at the clump (I recall quite a good combination of Rock 4 and small Alien in the crack where Severance crosses just above) or simply having the second simul-climb the bottom easy bit to allow the leader to reach the belay, all suggest that something longer than 50m isn't absolutely necessary.
Otherwise, I'm guessing that 50m should be fine. I say "guessing" because I actually used a 70m on all these routes; as guesswork goes, though, it is at least reasonably informed! First off, on Coastguard Slab, the extra length took me all the way to the railing - not, on this occasion, having a spare rope with me to pre-rig. Abbing for the gear with the rope rebelayed/equalized to a hex in an obvious crack in the outcrop atop the route, I got back to the start in the gully with about four metres to spare. It's probably between fifteen and twenty metres from the outcrop up to the railing, which puts the pitch length at around 50m or possibly a bit less; the second might have to move up the odd metre but, again, it's all pretty easy low down. For Severance I had the pre-rigged rope from the railing, so obviously had loads of the 70m left over at the belay under the other small outcrop (stake, sling draped over the flat top, possibly the odd nut); with a 50m it may be necessary for the second to move across to the clump but, again, it's pretty easy there. Right at the top on all three routes, where the angle starts to lean back just below the grass, there seem to be rather more features offering protection possibility than are encountered lower down; it should be possible for the leader to place something half-decent thereabouts and clip into it while the second performs any required relocation.
I trust this all makes some sort of sense.
