Was it these blackberries, link above? Packaged in Serbia, it doesn't mention on the site if potassium sorbate has been used, if you have a pack in the freezer check, if not when in Tescos have a look at another pack to see if they have used ks. That might be your problem. Although residual bleach may also be, always a good idea to use a little citric acid into the dj and swish about to neutralise any residual bleach, baby bottle stuff is better like milton or another simliar product.
Don't think honey is the problem.
Those crappy airlocks hate them, get a simple bubbler for dj's. With those airlocks it is difficult to see activity sometimes.