Sorry to DaveR , Paddy and anyone else who wasted their time reading my post. I must hold my hands up --- I made a complete mess of it.
It was, I thought, the overnight demolition of one of the tea bars on the prom, close to the new development.
On looking again, closer, today I realise that the tea bar is still there. What I had seen was the foundations of one of the shelters which had been knocked down a good while ago. But the foundations could not usually be seen because the site workers cars were always parked on it.
Sorry again everybody. I will take more care in posting in the future mike