If we were in central Europe it'd be likely all stock of breeding age would have been infected. Because we're on the edge of the disease range they may have been ..... or not. The vaccine costs around £3.50 a head. If you have even just one lamb with SBV look at the cost of feeding the ewe in late pregnancy, possibly having the vet out for a difficult lambing due to fixed hocks in the lamb, or putting down the lamb and/or ewe if she's damaged during lambing. If the ewe goes you've got the disposal cost and, if she's a young one, all the work and money you've put into getting her to her first or second lambing, with virtually no return. Just crossing your fingers and hoping doesn't work for me.