THE sun shines and the middle boy is up on stage with his friends. The platform on which they are performing is the back of a truck with the side opened up. Behind them is the impressive edifice of the old brewery in Leeds, now a cultural centre known with good Yorkshire brevity as The Tetley.

The truck faces a grassy area across which flattened cardboard boxes are strewn. Some of the boxes have been refashioned into buildings, almost as if this were a refugee camp or people making creative do at a rock festival.

It is in fact neither of these. Instead this is a den-building festival. We don’t join in with the dens, although we might have done when our three were small. We’re here for the band. It’s been a while since the parental groupies were present. That was when our middle boy was 15. The band was called The Frizz and they played around York, including a memorable gig at the old Fibbers in York.

Our boy was on guitar and we went with friends to watch. At one point, he played a solo with the guitar held behind his head. One of the songs contained lyrics about being new in town and drinking in strange bars while looking for love. The incongruity seemed funny at the time, boys singing about being men. Our boy does that half-smile thing at the memory as we chat in the Leeds sunshine. His sister is along for the trip too.

Various bands have been booked for the day. We sit in the sun to watch the first band. They are very young and not at all bad. Up next is the Manchester band our boy now plays in, seven or eight years on from that first band. They are called Sonic Bliss Machine and he plays bass this time.

I’ve never seen him play bass and he is good, as is the band. But in a way I miss seeing him twirl out those guitar solos. It’s probably a father-son displacement thing. I always wanted to play guitar in a band but was never good or structured enough. There was an embryonic teenage band called Aardvark Zyrus, the first and last words plucked from the nearest dictionary to hand. We didn’t progress much beyond the name and a practice or two. Nowadays I strum at home, arrhythmic and alone.

Anyway, in the sunny here and now the band is still playing their set and we are eating our sandwiches. A man with a heavy-metal beard and a beer belly fiddles with the sound-deck, while the muscled compere prowls around with his microphone and his ready-made stock of crowd-teasing banter.

Then the set is over and our boy and his friends cart their gear from the impromptu stage. Members of a young jazz-funk outfit are waiting in the wings. The compere is ready to do his thing again. One or two of the parents are tiring of building dens and are drinking beer instead, a fitting tribute to the industry that once went on here. A boy aged perhaps two continues to dance, little legs jiving, while a straw trilby protects him from the sun.

After ice-creams bought for us by our student daughter, we leave the boy, happy to have seen him play again, and head home. Without getting lost this time in the never-ending one-way loops of the Leeds traffic system.

Later, much later thankfully, long after the bands have gone home and the cardboard huts have been abandoned, it rains. My God does it rain. I take our daughter to the station during an impressive downpour. The drive back is the scariest of my life, the rain so heavy that the roads flood instantly and the windscreen wipers weep with the effort of keeping things clear. The sky is midnight black at eight on an August evening. A headlight bulb went earlier in the day and the one-eyed car goes slowly home, more boat than car almost.

It was like one of those rainstorms you see in films when everything looks just a bit too over the top. No rain ever falls that hard, you think. Now I know that it does.