Best time is autumn - you could plant them now, but you'd need to keep them well watered yourself (assuming we have 4 dry days on the trot at any point). Planting in autumn means you don't have to worry about watering - although an indian summer might mean you still have to for a while, but once it gets to November, it won't be necessary.

Hostas in pots i found were a lot of work,they constantly need watering to look good and in turn grow and need re potting or dividing frequently.As long as the slugs are kept at bay they are pretty much bomb proof and will do well in the ground as suggested.

thankyou to dgw and to all who responded to my question, i shall give it a go and see how i get on.