@Hennightmare OK so this is a difficult one. Just because the booking site says it when you looked after your entry had been refused upon arrival, was it there when the MOH booked? By the accommodations own admission they had a problem a few weeks before and maybe they added after the MOH booked in response to events with the previous party, in which case they should have honoured the MOH booking.
However, if upon booking, the website clearly stated no single‑sex groups / no hen or stag parties, then the MoH knew this, she booked anyway because she’d seen other hens on Instagram and assumed she could chance it. That’s not a misunderstanding. That’s a deliberate gamble. The landlord doesn't need to check as its in the t&cs, and just as the MOH, they have every right to turn you away. They do not need to double check your intent.
And when you gamble with other people’s money, you take responsibility if it goes wrong.
I think that if the MOH booked with a credit or debit card she should make a claim via them, providing all paperwork, the advert for the accommodation at the time the booking was made, and the fact it did not say no single sex parties - which automatically by definition rules out Hen/Stag does. And the booking site as it looks now.
The location of the planned event is irrelevant, some hens want a boozy weekend (Blackpool), others want a base for country activities, a spa or just a girly weekend.
For those asking why the owner didn't query a booking for such a large group, I think that is pretty obvious. If you are a family of 4, you look for and book accommodation for a family of 4, if there are 10 of you, you look for accommodation that will accommodate you. Therefore if a landlord has a property that sleeps, say 12, and gets a booking for 10, why would they query it?
Also, for those asking why they didn't let some of them stay, are you mad? Whether there were 4 o 10, the rule was no hen parties, they would be weakening their stance.
If they find in the MOHs favour, you all get your refund and I would consider going to the small claims court to claim for further losses is there were any.
If they do not find in the MOHs favour, then the MOH needs to accept her error and refund you all or those that request refund. Because the owner enforced a rule that was clearly stated, had recent damage from a same‑sex group, refused entry exactly as per their terms and refused a refund because the MoH knowingly booked against the rules. This is not “bad customer service”. This is a business protecting itself from a category of booking that has caused problems. The fact that some hens have slipped through in the past doesn’t magically void the rule. It just means the MoH assumed she’d get lucky.
If she’d booked a venue that didn’t allow children for a child’s birthday party, or a restaurant that didn’t cater for allergies for someone with allergies, everyone would agree she was responsible. This is no difference.
If the latter is the case, then YANBU, she chanced it, she lost, and she should put it right. But that is yet to be confirmed because the venue could have added those requirements post booking but I doubt it.