Thanks everyone. I reckon that the lids are the problem and some of the plastic seals look a bit suspect. SOOO my neighbour reckons that if I scrape off the mould and boil it all up again, stick it in jars right up to the top and then fit the lids (no plastic seal just wax paper) that should do the trick. Actually tasted some, minus the mould, and was v nice. So all I have to do is wait for a rainy day and get cracking, which shouldn't be a problem up here in aberdeenshire. It's very labour intensive isn't it?
This is my first attempt at jam making - hopefully next year ill have lots of blackberries which will be a bit easier!