Looking at the clothes and hairstyles, it looks like an Ian Allan trainspotters day out.

Pete
I once went on an Ian Allan Locospotters Club day out, and let me assure you we were not dressed like that (That day was – in my honest opinion – the nearest thing to a poorly controlled riot that I’d ever been near, due to a minority, but very visible, bunch of ‘oiks’ – it was possibly the day hooliganism was invented, but that’s another story).

Notice the S/A Pioneer to the left ?