I am shooting in the city of London this weekend. I am based in the USA and usually use cake batter for gunge and cool whip and choc syrup for cream pies.
What is the alternative for making gunge in London, something I can easily get in tesco or sainsburys, was thinking custard and I know there is whipped cream but what other gunge substitutes do you have there? Thanks in advance, will share some pics here from the session!

Rice pudding, angel delight, trifles, yoghurt to name a few

I am looking for a gunge substitute that looks like cake batter consistentcy!

You could try yorkshire pudding mix - should give a similar consistency when mixed with water

Yes, custard, whipped cream, yogurt, angel delight or rice pudding can all be used.

However if you a type of cake batter/gunge. As you may be visiting Tesco/Sainsbury's you could look for some xanthan gum (in the home baking isle) and mix with warm water, children's poster paint can be used to add colour. Or you could just use flour and water, this will make more of a batter (again poster paint to add colour). Be careful as this can be a nightmare to get out of hair.

When mixing the xanthan gum or the flour you will most likely get lumps. But if you leave to settle, then give another vigourious mix, the lumps should come out.

Hope this helps. Enjoy