Because of this, instead of charging a group rate and leaving it to individuals to organise into groups, I'm going to change the pricing.
I think £10 per person per hour is reasonable. That's £30 for a standard 3-hour session per person. I recently accepted £60 for a 2-person game that lasted 3 hours.
I also think a group discount should apply, so if you're a group of 4 or more people, up to a maximum (soft maximum, so it's negotiable but advised) of 8 people, then the price drops to £7.50 per person per hour. This would be a total of £90 for a 3-hour game for 4 people, exactly the same price charged for 3 people for the same amount of time. So it's a good discount if you come together as a group and pay all together in one go.
What do people think?