I am sure you could give them a light prune or take all the leaves off that have the black spot on, then you would have to burn the leaves and I am sure if you get something to treat the black spot, the roses will bounce back, they are pretty hardy things. I sometimes put banana skins just around the roots and cover with some compost, you do get a lot more flowers.

Personally I'd prune them asa if it were February/March now . They'll recover and flower 6 -8 weeks later than usual. Spray as soon as new leaves are out to stop the black spot and give the a mulch of well rotted manure or some fertiliser.

Roses are very tough and should recover well.

Agree with Anchorman - prune to increase airflow between the branches, remove anything dead, dying, damaged or weak and crossing branches which rub each other. Apply Toprose at the roots, turning it in, and if its okay with the owners to pay for it, apply a mulch of composted animal manure or soil conditioning compost around the roots. Then spray thoroughly with Roseclear Ultra, repeating fortnightly. If you use Toprose immediately, you can just about have time to squeeze in another dose of it after 6 weeks, although technically, they should not be fed with such a product past early June.

Thanks very much for the advice. I'm going to gather up the necessary and pay them a surprise visit next week!