Two things. First you definitely have an infection there. It looks a lot like lacto, though it could easily be something else. I dump infected beer, but some people swear they'll get "better" with age. Up to you on that one. Also, your fill level on those bottles looks very low. Try and get about 1 inch of space between the cap and the beer, as you should get a more stable carbonation in the bottles.
Never tried Muntons dried yeast before, though I've heard horror stories about it. Maybe next time try using one of the safale or fermentis dry yeasts (S-04, S-05, Nottingham) if you haven't done so.