Gunipigs

gov.uk site says you don't need to register them but you need a certificate from your vet to state health.  if travel is via france they could stay  in car if you intend to come by ferry via Spain you need to ask Brittany ferries what the policy is on taking them into a cabin as  it's not allowed to access the car deck during the journey so you couldn't check on them.  they allow cats and dogs in pet friendly cabins but they are always booked well in advance. whatever do not just bring them as they will probably be taken away at the customs point if discovered.  we once brought a budgie back from Germany to the UK and had to go through hoops to do so including signing a form saying we would not eat it!

Not quite sure what a gunipig is ?

it's a mistype of guinea pig of course.

Years ago I travelled to Spain with a chinchilla. I remember asking my vet what was required, so would advise you to do the same.  It was pretty easy, a simple bit of paperwork I think, but months later the climate proved a problem and I'm afraid Crombie didn't survive the summer heat.🥵