If you planted an early variety then there is probably time for them to grow and form tubers before autumn. A late variety probably doesn't have time to mature.
Your main problem at this time of year would be the threat of late blight as this gets going most summers, when it's wet, and is the reason why the 'second crop' varieties sold by some enterprising seed companies were always a problem.
If blight is threatened in your area, give them a good spray with bordeaux mixture as a preventative treatment.

I 'think' most of England is still suffering from a drought. If this is the case you will need to water well to get the potato plants to actually produce potatoes. Good luck in any case.