There is a UK Government entity that deals with this area.
Animal and Plant Health Agency (England and Wales)
planthealth.info@apha.gov.uk
I doubt this will be an easy or cheap process. However I do understand why you might want to try as it can't be a nice thought having to sell them. Also you will no doubt be aware of the difficulty getting new release orchids. Since Brexit the sources for orchid growers have been severely limited and there isn't the amount of orchid nurseries there used to be.
As an aside Burnhams Nursery is a good source for plants and there is another one just opened in the South by the man who ran the Writhlington Greenhouse Project. I can't recall the name at the moment but I'll get back to you with it.
At the very least you will need phytosanitary certificates and I think I've seen some rules about the weight of the total import which will probably mean another level of compliance.
I have heard second hand stories that these certificates can be time crucial too, so if the plants get held up it could cause problems.
Granted the second hand stories were about Australian Customs but best to be prepared and it gives you a question to ask you may not have realised needed to be asked.
I expect even if you dot all their Is and cross all their Ts you could come up against someone who interprets the rules in a different way and refuses entry.
Still it costs nothing to ask the authorities.
Please let us know how you get on.