please empty your brain below

Sounds oh so typically British...
If I had booked the tour, expecting a maximum of 15 and 10 extras turned up I'd have been right pissed, to be honest.
I'd have told the chancers to go away and the self-righteous women would have gotten a piece of my (limited) mind.

Maybe that's why I don't work in customer services ;-)
I turned up an hour early to a venue for a booked tour, but no I couldn't hang around in case there was a spare slot -- because, security.

So, there's your excuse in future -- security.
All this needed was for the guide to have had a list of bookings, then to have checked names/numbers against the master. Not on the list, not coming in (takes me back to the Marquee Club in 1978...). Agree with Grumpy's comment, too.
Surely the rule should be no proof of booking, no entry. And then first-come, first served if they want to allocate spare slots.

I'm sure the woman with a terminal case of entitlement is used to getting Very Cross on a regular basis. Someone needs to give her a Hard Stare.
Something a bit similar with Modernism in Metroland tour (Sat am) - max 25 but by 10.00 about forty present. Tour organiser Josh (excellent) gave in to the inevitable and we trundled off. This tour didn't require pre-booking so this outcome was predictable...

The problem of pre-booking is that as slots reduce to take up, that can throw out the rest of your day - I had three venues planned for the Sat (two in outer London, which means travelling time rather than more visits) and HAD to be on the morning Metroland tour to visit the other two.

Nevertheless, another bloody brilliant Open House - roll on 2016.
Ha, I encountered some chaos at Walthamstow town hall. The Open House guide hadn't turned up. A councillor who happened to be holding her weekly surgery bravely stepped into the gap. She knew very little about architecture, but did a good job of showing us round. The poor security guard downstairs had no idea what was going on, and just waved more and more people upstairs to try and find the group. We ended up with people wandering willy nilly and getting cross at the lack of organisation. I felt very sorry for the councillor who had to cancel her surgery in a bid to help people out, only to get a string of irritated comments (we did give her a round of applause at the end, though).
At Trellick, they maintained a first-come-first-served waitlist. If you turned up without a booking, your name went down on the list.

When the tour was about to start, any empty spaces were filled from the waitlist... overall it seemed the fairest and most pragmatic way to do it.
Applause to the Trellick Tower. That's the way to do it.

Here are the notes from the Metroland tour. They seem to have expected more than the "maximum" number.
If there is a booking system then that is it. No excuses, no chance of getting in without a booking.
How is that so difficult?

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