Can someone tell me what this is and if it's worth trying to save these roses. The new growth appears to be very poor
Judging by the gnarled bud union and the amount of lichen, these must very, very old roses. If they were mine, I would replace them with new ones. But some will probably have more knowledge and know how to remove the lichen to give them another chance.
I'd agree with Sue. The lichen is merely an indicator of their age and is not harmful in any way. It does show you have excellent air quality though.
If you are happy with the flower power then keep to your current care regime. If flowering is weak then take out, and grow something else in this spot ( unless you replace lots of the soil ) and plant your new roses elsewhere.
This will help avoid any future rose problems.
SusiB, the new growth is healthy enough, but they are old, they may do well with a good feed and a mulch. The Lichen you can leave in place if you want it'll do the roses no harm. If you do decide to remove them, you can replant roses in the same bed if you add mychorrizal fungi to the planting hole along with plenty of Farmyard Manure.
The old advice of rose sick soil is out of date, the mychorrizal fungi replace what the previous occupant used up.
You can still get replant disease even when using mychorrizal fungi. You plant inside a big cardboard box placed into the hole and fill this with new compost (loam based), buy the time the roots reach the sides of the box it will have disintegrated and the plant will be well established