Might be worth treating it with evergreen moss killer & lawn feeder 1st. It will turn all the moss black within a few days, then at least you will be able to rake out the moss & see how much you have / grass is actually there. You may be lucky to have some grass underneath which is simply getting suffocated by the moss. You might have to do it a couple of times in the next month or so but usually evergreen is very good at killing moss & you will be able to re-seed. Would be a lot less hassle than re-turfing (unless it's a really small area).

Agree with the above - also bear in mind the causes of moss overgrowth - shaded lawn, north facing, irregular cutting, not fed, needs de-thatching and spiking, and drought in summer - all of these will cause moss, and some of these things can't be avoided and will occur again in any new turf you lay. Treat regularly with something that feeds the lawn and kills moss - follow the directions on the pack.

...and don't compost the raked off moss as this will only spread it around the garden.

So grateful for the answers, I'm going to be busy! Sunnycote