The only one I can think of that resembles hydrangea for flower form, and a lacecap hydrangea at that, is Viburnum plicatum 'Lanarth'

Thanks for that Bamboo, I'm not sure thats it. I see them all over Jersey in parks, they sort of look like Hydrangeas but the flower seems more open and most of them seem to be a very vibrant purple colour and looser flowered, if that makes sense. I think it's of the same family but a variation. I thought it began with M but then saw the name macrophylla but that just comes up with the regular Hydrangea pictures.

Take a photo and post it on here for ID

Sounds like big clumps of Agapanthus, but without a photo it's real guesswork.

No definately not agapanthus Beattie - we have a plethora of those here, should be called Agapanthus Islands !! I'll have to go out with the camera tomorrow, I don't have any of them near to where I live.