Thanks for all your advice lads -
I went for the Yuasa battery in the end as I got a very good deal for one through a friend. Apparently you need beware of imitation Yuasa batteries for sale on the internet tho- thats what I heard on the grapevine - don't know how much truth there is in that - but wouldn't surprise me tbh. Will add another post soon, to report on how I get on with the new battery and give my verdict !!