AIBU not to invite work colleagues with plus ones to wedding reception?

[Pleasehelpmefindmydress]

We're having a small wedding in August and the guest list is becoming a bit of a headache.
The venue can seat 50 for a sit down meal and 75 for a buffet - we're leaning towards a buffet so we can invite more people.
I'm inviting about 10 work colleagues - but if they all accept, I can't really open it up for them to bring partners as well as that will be nearly a third of our guests. I do know some of their partners but not all.
Would it bother you to get an invite that doesn't include your OH for a work colleague's wedding reception?
Ceremony is at a register office so family and a couple of close friends.

I think if you invite anyone to a wedding you need to invite their partner too.

However, if you behave a conversation with them about who's invited, they might agree they'd rather come without.

There's no overnight stay involved. We're a close bunch and I've worked with most of them 15+ years to give some context.
DP and I travelled 150 miles for the wedding of one colleague (two nights in a hotel) some years back. Been to weddings of two others but they were 100+ people receptions.
I could extend the invitation to everyone informally, and if only half can come (the five I'm closest to I'd imagine) I could then include their DPs.