Unfortunately I'm not in the country that weekend to attend but I've just been nudged about this event by a work colleague and figured it might be of interest to others:
The gorgeous Crossness Pumping station, near Abbey Wood, South London/Kent is only open for a few open days this year and on Sunday 26th June they are holding a Steaming and Historic Transport Day.
Not much info on the site as to what exactly is taking place but I assume the beam engines will be in operation. If you haven't been there before, I strongly recommend it as the place is absolutely stunning!http://www.crossness.org.uk/
Its a tad out of the way to get to by public transport but they will be running mini buses from Abbey Wood station during the open day.