I forgot to add DO NOT get a guinea pigs teeth cut. Yes, their teeth do constantly grow but you dhould put some wood in the cage to gnaw at. Also, by providing hay daily, their teeth should stay at a good length.
Hay should not really be used as bedding because it gets soiled easily. Pigs (who would) don't eat hay that they have urinated or pooped on. Try using megazorb
www.megazorb.co.uk or vetbed from ebay, or fleece.
You said hutch, so I am assuming you're keeping them outside? It can get cold overnight in England, so I recommend bringing them in at night and during september to April