In reply to BoulderGoat:
FWIW, if the weather's been good for a while (and hence the rock is fully dried out) then Southern Sandstone is worth considering and is also day-trippable from Cambridge.
There isn't much guidebook information about whether you can set up a top rope at any given crag because you can almost always set up a top rope at any given crag, provided that:
a) the route lengths are less than half your rope length (assuming you want what's pedantically known as a bottom rope)
b) the top and bottom of the crag are relatively accessible
c) the routes don't all wander all over the place and
d) you can set up reasonable belays on the routes as trad routes.
a) to c) should be obvious from the guidebook, and d) is the case almost everywhere to the point that you'd expect a guidebook to specify if it wasn't. Explicitly specifying that "it's possible to set up a top rope at this crag" would seem like explicitly specifying that "it's possible to climb at this crag wearing a yellow T-shirt" or something.
Again, the reason that you're getting some puzzled responses on this thread is probably that this sort of stuff seems obvious enough that people are worried, rightly or wrongly, about someone who doesn't seem to be experienced enough to be aware of it taking out novices...