Potato blight.... got it for the first time this year! Have eaten the potatoes (lovely!) but concerned there may be something in the soil. Just about to put purple sprouting in the raised bed. Do I need to worry? Should I treat the soil first?

Should be fine as they are brassicas and will not be affected by any blight that might be in the soil. Just make sure you don't plant potatoes there for a few years. One of the reasons for crop rotation is to prevent a build up of, for example, blight in the soil.

As important as anything, watch out for any 'volunteers' (plants growing from tubers left in the soil) next year. These certainly can carry blight over from one year to the next. Pull out and destroy any you see immediately. Don't think this will just give you a few extra potatoes.
There is a lot of debate about whether blight can survive in the soil and whether you can compost blighted leaves etc. I'd say you can do this if you get high temperatures in your compost heap, but I think infected tubers are the main way the disease is carried over from year to year.
To be really safe do what Moon grower suggests and rotate your crops as well.

You do not actually have to dig up the potatoes if you remove foliage at the first signs of blight. You get a smaller crop, but the tubers are clean. We always burn all potato tops to avoid the spread.

Thanks all for the help.