I get my fly gutload from mantis place - which seeing as your in the UK is probably not an option - but it's a mixture of powdered sugar, powdered milk brewers yeast and bee pollen- plus some other ingredients - I have given them bee pollen when I misplaced my bottle of fly food- you have to grind it up real fine (i stuck it in an old coffee grinder) - I also have used bug burger when I couldn't find any of my fake water -
This morning I had a bit of an accident with my blue bottles and let loose more than I had intended in Clifford's cage - She cleaned up my mess before I got out of the shower- she's had the first 5 in less than 30 seconds-