It was a Chris Barber jazz concert, I think, 1954, although I can't now be sure.  I was there with my girlfriend and we had booked tickets in advance.  When we got there, there was some mix-up over the seating and we had nowhere to sit.  (Several of us were in the same boat).  Finally, someone brought out some spare seats from behind the stage and arranged them in a semi circle on the stage to either side of the band.  We spent the concert sitting on the stage right next to the band.  Fantastic!  I always listen especially closely to the Chris Barber Royal Festival Hall recordings from the 50's to see if I can hear myself shouting and applauding!