In that case EXPLAIN your reasoning, and by the way the Terms do not necessarily rule out Groups and Singles but request that such bookings are made 7 days in advance in the first instance, prior to confirmation. The company obviously have their reasons and have no doubt taken Legal Advice as I'm sure they have come across this before.
If the " Disagree " is related to my use of the apostrophe then explaining the reasoning would educate both myself and others.
Firstly, I wasn't the disagreer, but offered a potential explanation for the poster who did.
The T&C's are reasonable for groups - different scenario, not a protected characteristic - and fairly standard.
The treatment of singles is different to a couple as advance agreement is required before singles are accepted. So, if two vehicles arrive at the same time, unbooked, one containing a couple, the other a single person, and they allow the couple to stay, but turn away the other away because they didn't abide by the 7-day rule (which only applied to the single camper). This different treatment is discrimination, in this case against the single person. Now that person may be married or in a civil partnership and traveling alone, unmarried, or perhaps widowed, it matters not because the majority of people affected will be unmarried.
Discrimination may be unlawful if it is based on a protected characteristic as defined in the Equality Act and it is not one of the circumstances which are amongst the many exceptions. Marital status is a protected characteristic BUT not for the provision of services, only for employment.
So they're off the hook then?
No, not quite, since statistics show that significantly more people between the age of 16 & 29 years old are single, so the 7-day single rule indirectly discriminates against people by age. There is a difference in the proportion of singles by gender too - so this could also be indirect discrimination. It's a minefield!
They may have had legal advice on their T&C's, but they may not have revised then post Equality Act 2010. Many T&C's are old, copied from other places, or just plain wrong.
The chances are no one will ever challenge it in the court since legal aid is so limited and the discrimination indirect, so those affected will feel aggrieved, as the OP did, and move on, perhaps starting a post on a forum for an interesting exchange of opinions.
I hope you will accept my reasoning as to why I consider the 7-day rule for singles appears unfair and may be unlawful.