Weird gelatinous substance in highland bog
So the One show did a magazine piece on this the other day; a scientist did some DNA analysis of some of it. 

The conclusion was that it's frog jelly (full of frog DNA). Apparently frogs have glands full of the components of the jelly in sacks in their bodies, when the sacks come into contact with moisture it expands massively (same process that allow them to produce frog spawn). When a frog is eaten (by a bird or fox) the jelly expands on contact with any moisture. The animal eating the frog either vomits it up or doesn't eat it in the first place and voila.