I was told that they were supposed to detach themselves when they were ready to harvest, but now someone else has told me that that isn't so, and that they should be picked now and left in a cool, dark place, and then they will survive for months. Please bear in mind I only have experience of this part of the world which is probably a bit warmer for now than yours is. I think if there is a frost forecast, or the nights where you are are getting decidedly chilly, pick 'em quickly, otherwise leave 'em in the sun (if you have any).
If you pick them now, at least you can then clear the beds of all the mass of tatty stems and leaves, and dig them over.

I'm planning on growing Pumkins next year, so have been reading up.

You leave the fruit on the plant for as long as possible but before any frosts. When the stem cracks and the skin is very tough, the fruit is ready to be picked. Cut fruit off with a long stalk to allow them to feed.

keep indoors at 27-32ºC (81-90ºF) for 3-4 days to harden off. They keep for up to 6 months in a garage or shed.