Easy to remove Ian, how I'd do it is clean the paving first getting the dirt, algae and easy Lichen off, spray with a 3:1 mix of Hypo, let it dwell for around 20-30 mins, work in sections so you don't loose time etc (if it's hot at the weekend keep the mix wet so it doesn't dry out on the surface) then wash off. You should have one happy customer.