To think you should invite your partner if this happens?

No need to call your partner in this scenario because they most likely would have made their own plans for the evening whilst you were out even if it’s just a quiet night in and an early night.

I can only see this being a problem if the person at home is very jealous and likely to kick up a pathetic stink when they find out someone else’s wife turned up!

Surely this is discussed ahead of time? We (my friends and I) socialise as couples, families and as just us friends with a reasonably even split. Any time something is suggested, we clarify who’s invited in that context.

Does it actually matter why she's asking?

Presumably that wouldn't change your opinion either way!

OP, it wouldn't (hasn't previously) especially bothered me if someone has brought their partner along. But I wouldn't then contact my partner at home/doing their own thing and invite them to come. Nor would I expect to be invited.

My partner has a friend who has been with his wife for 45 years (met at 15 and now 60!) They are pretty much joined at the hip and go.everywhere together. No one minds and everyone expects it but I'd rather not be like that and so I wouldn't expect an invitation and I wouldn't issue one.

No, I wouldn’t invite or expect to be invited. Why would I want to suddenly change my plans just because one of DH’s friends has brought his wife or invited other women? Unless these women are my friends (which they aren’t, because my friends would have told me they were joining and invited me themselves) I’ve no reason to want to spend time with them - and vice versa for DH and my friends.

Neither of us would invite the other, and we’d both have a moan the following day about the friend(s)’ inclusion of people who shouldn’t have been there.
There’s no ‘politeness’ in a later-than-last-minute invitation to join a messed up dynamic.
It just smacks of insecurity.

Exactly

You'd go home or go and sit by yourself in a different pub because there's a man there?
Bit of an exaggeration.

No, it wouldn't make a difference. Unless the partner is good friends with all, but then why wouldn't they be invited in the first place? Odd.

I wouldn't want my husband if I was with my friends, no offence to my husband at all, but I dont care if others have theirs i dont need see the problem of partners, I couldn't do 'girlie nights' or whatever people want to label them

But i also dont understand why people cant have a night out without their partners either it is weird to need to be glued to them

Saying there are extenuating circumstances implies this happened. So why not just be upfront?

Why would you want to get ready to go out and join people that are already out and didn’t invite you when you have the house to yourself?

This EXACT situation was what I was in last night. A group of women meet one friday evening a month. This group started as a 4 and is now over 20. We meet because where we live, we are all expats , most have small businesses or do volunteer work, so we network. It is nice to meet english speaking women for friendship, when so many of us are, at best, have a hard time communicating in the language here. Anyway, it is great $1000 pesos (about 12 gbp) get a welcome drink, a cocktail of choice and a appetizer buffet. Different restaurant each month to introduce us to more choices for ourselves at other times. Anyway to get to the point. Last night I saw 1 of the women's husband on the patio with 2 other men. I asked her if "Steve" was here? she said yes, he drove her but he was on strict instructions to stay outside or go to one of the other restaurant/bars in the area for the duration. So I would not consider calling my husband to come join, if one man (or woman on a guys night) was rude enough to crash the fun, as what would be the point of girls/guys nights?

I don’t think these dynamics have anything to do with a DP …. It says more about the friendship group that they see a girls night and just invite a DP… I’d be pissed and in the past used to say ladies where should we go as a hint ….

Yes not theoretical either you or DP have baggage about friendship nights out and are now setting rules. Dangerous your new partner is not the same ex-partner

I have a different opinion: if it was meant to be a meeting with my friends and suddenly I found that OHs were invited, I’d be cross with friends for changing the dynamic and probably leave early.
If my husband went to see his friends and their partners were there unexpectedly, I’d not give a hoot as I can’t stand his friends anyway (and would just assume the feeling is obviously mutual 😁).

So without people adding specific extra context like “what if you’ve known their spouses for years too” or it’s a mixed gender group generally (which wasn’t the question - the question was YOU'RE GOING OUT WITH JUST THE BOYS/GIRLS AND TURN UP TO FIND THE OPPOSITE GENDER THERE TOO)

I’d 100% reach out and ask my other half if they wanted to come too as it turns out all are welcome. If they couldn’t or didn’t want to come then fine. Id think it was weird that their friends failed to tell them it was mixed OR that they knew and failed to tell me?

I’d only ever have not invited my husband because it would have been weird to do so eg no other partners coming.

Anyone I know who didn’t reach out to their other half is strange. I say this as in my experience it’s usually men that avoid inviting partners to couples or mixed group nights out. I’ve had multiple boyfriends do this in the past and usually one (or several) of the attendees will reach out when they arrive without me to ask why I’m not there too because it WAS a “bring your partner” event and it’s clear my partner just didn’t want you to go. That’s a whole other conversation you need to have with your partner. (Alternatively, if everyone else but your partner was asked to bring their partner, I’d question the friends not liking me?)

If it were a mixed group, eg we’re all friends from school (so you go out mixed with no partners invited, just friends) then no I’d not text them to come because they’d have known before I left I was meeting “people from school”. I’d however find it strange at my age that people didn’t just in invite partners and integrate everyone, which is what my friends do if it’s not “just the girls” but that’s just my friends ! People with kids are different as sometimes someone is needed to babysit, but everyone would be welcome!

Hope that helps.

Exactly

Totallly depends. If the get together was just 5 minutes away, then possibly ring up and say hey Dave’s here too, why don’t you come along. If at a restaurant or something in town then wouldn’t bother, but when I got home would still feel that it was annoying that the girls night had been diluted, but not see a reason to dilute it further.

Hopefully I don’t have any friends who would just bring along a spouse without saying so! If DH was free I would always ask the friends I was meeting if we are bringing partners. But this is a non issue for us as we have small kids so we are never’free’ to go out at the same time as each other unless we pre-arrange a babysitter for a night out we have decided to spend together

If I went on a ladies night and someone bought their husband/boyfriend, I’d be pissed off and probably text my husband “so and so has bought so and so. WTF” and be very peed off and definitely wouldn’t ask my husband to come out then and I’d ignore the uninvited person.

So it wasn’t a chat
it was you raising this setting the rules!
and DP agreeing with you

No i wouldnt invite my husband and no i wouldn't expect or want to go myself

so if i go out on an arranged "ladies night" with my women friends, and one or more brings their spouse? If the spouse is someone i know, and is a woman, for sure no issue.

If it is a man when we planned a "ladies night"? I'd go home or go somewhere else.

Oh they’ll be a reason Op, a specific reason, why you and your DP was discussing this.