I have strange lumps of jelly appearing in my garden pots and have no idea what they are.

I first noticed it in my pots in the front garden (west facing) in late Sep/early Oct and have just noticed it again today in the back (east facing). I googled 'jelly lumps in pots' and found this rather long and somewhat bizarre BBC Scotland link

http://www.bbc.co.uk/scotland/outdoors/articles/jelly/

Living in 'central' London I think I can rule out stag semen and my logic (just about) discounts alien snot, frogs cannot get into my back garden and I doubt planes would eject just two 1cm squared lumps of 'waste'. I'm not going down the chem-trail avenue.

I'm more predisposed to believe the fungus answer or some sort of water-retaining pellet in compost, although the west facing pots would seem to discount both to a degree.

Anyone able to shed any light?