Hi Gary,
I can confirm that there is no caravan sites on Holy Island itself, however the following Caravan Club CL, is situated approx half Mile from the start of the causeway, across to Holy Island. I have not stayed here but had a look in last year, its along a long drive way upto this farm, a little small but looked nice to me and would try it in the future..
R C Rogerson & Son
Brock Mill Farm
Beal
Berwick-upon-Tweed
TD15 2PB
England
Telephone - 01289 381283
Email - brockmillfarmhouse@btinternet.com
WebSite - www.lindisfarne.org.uk/brock-mill-farmhouse