Those sort of mildews & funguses are not really connected with one type of plant, they're in the soil. Some plants are more susceptible than others though so will display noticeable symptoms.
They're often made worse by the weather, for example sustained dry but humid conditions are worst for it. Keep the soil moist but don't wet the leaves when watering. Mulching helps along with pruning for good airflow.
Some people use a milk spray at various dilutions & there are chemical products available but whatever you use catching it early is key.
If it's any reassurance there won't be many UK gardeners that haven't suffered from it

There is a devastating powdery mildew of aquilegia currently going the rounds. it has destroyed one of the national collections of aquilegia.

I posted about this a few months ago as I noticed my newer ones had succumbed though the very old varieties hadn't [yet]. burn or compost in a council garden bin but don't compost your own infected plants as the compost wont get hot enough to kill the pathogens.

https://www.rhs.org.uk/Advice/Profile?PID=866

There are many subspecies of these fungal diseases so they may have been transferred or they could be a different variant.
General advice and info from the RHS if it helps.

https://www.rhs.org.uk/advice/profile?pid=253

Thank you both for your replies and the links. I think I had better be safe and dig them up and plant something else in their place. Perhaps a few more foxgloves for next year!:)

That's a shame. Could you pot them up & put them somewhere else to see what happens?

Thanks for your suggestion Darren. I went out between rain showers today and there are a few new leaves already unfurling and they look healthy so far.