Pac a Mac recommendations.

Rab Downpour is a little over budget. Can be had for £120. Bought mine last year for dog walking and it's been excellent. packs small and has been tested as sufficiently waterproof (dog was less amused). Was less impressed with some of the other options as I wanted small pack size and the Patagonia fell over on that score.

I got a waterproof I think from the cycling section in Decathlon, it has a hood and the back is extended like tails of a suit jacket.  It's fluorescent orange but it packs down to nothing and it certainly wasn't anywhere near £100 or I wouldn't have bought it.

On a similar vein, I'm looking for a non-technical long waterproof jacket for cubs camp in case of a downpour. Simple/ non too technical, good coverage, waterproof. Decathlon probably has the thing but any other ideas before I get there?

I’ve been using a hooded zip jacket from Millets, a Peter Storm one for a few years. I wore it at work over the top of my Buffalo Special 6 and it did what I wanted it to, keep the rain off the Buffalo, which would get slightly damp on the surface after a 10-12 hour day outdoors. It cost me £20, about what I pay for four pints when it’s my turn to pay. 
I bought a second one in Bath several months ago when it came onto rain, and wore it over my ultralight down jacket, and it worked perfectly to keep me dry. 
Honestly, for £20, it’s a perfect jacket to stuff into a bag on a just-in-case basis - they do come in a bag, but I always forget to put it back into the bag, I just throw it into whatever large bag I’m using at the time.