Still getting handfuls of raspberries. The canes were already on the allotment when I started tending it. I had assumed they were summer fruiting raspberries because that is when they first start to crop. In fact they have became more productive in the past month or so.

 A fellow allotmenteer who is wise in the ways of raspberries provided what seems a likely explanation. Apparently if you do not cut autumn fruiting raspberries down to the ground over winter (as the books recommend) they will start fruiting in summer. I tend to leave the bare canes standing and perhaps they are indeed of the autumn fruiting variety.