I am having trouble understanding the tapeworm rules and going to France for a holiday for 8 days
Is it right that we have to have him treated by a vet and passport stamped 24 hours before we go and then have to have him done again by a vet in France before we come back as we'll be gone for more than 120 hours?
Yes that is correct. Youcan purchase the wormer here but must be witnessed/administered by a vet within 120 of return to the uk. This is to prevent the spread of a type of tapeworm that can pass to humans which thus far isnot present in the uk.
Your dog must be treated against tapeworm before travelling back to the UK but not necessarily before leaving the UK. However, there may be other requirements for travelling which are specified by your carrier. They may request a vet health check within 24 or 48 hours before you leave home but all carriers have their own rules so you need to check.
"Tapeworm treatment must be administered by a vet not less than 24 hours (1 day) and no more than 120 hours (5 days) before the dog's scheduled arrival time to the UK. Treatment date and time must be recorded by the vet on the EU pet passport."