Is a couple plus a friend sharing a property an HMO?

I always thought 2 households could occupy one property but reading the latest information, it look as though I could be wrong. It seems that 2 individuals can share a flat but a couple plus 1 friend makes the property an HMO. Is that right?

What other measures should I be taking if the property already has an annual gas saftey check and a valid 5 year EICR as well as hard wired smoke alarms?

I get a lot of people (especially in the current climate) asking to share a property with a friend. I am right to be turning them down as it would make the property an HMO.