Depends on just how weedy it is and what type of weeds they are. If it is a neglected allotment with nettles, heavy clumps of grass, rosebay willow herb etc then it would probably be best to take all the weeds out. If it is not too bad then just turn the weeds under and leave them. This is how we treat our established plots. I would still remove any seed heads and stuff like buttercups as I went along, though.

Thank you! we had been clearing weeds regularly but they seem to have gone mad in the last couple of weeks. will clear seed heads as you suggest and dig the rest over.

Catkin, you need to dig out any taprooted and perennial weeds, annual weeds can be buried one spit deep.
If you are on clay, leave the ground rough for the frost to break down. In the spring you should have a fine tilth to work with without digging again. Light soil will go flat with heavy rainfall and needs digging again.

take out all deep rooted weeds by the root dandelions etc. leave any root and they will grow back , and dont kill yourself digging mark a square off that you can manage comfortably then do something more relaxing sowing seeds or have a cuppa with your favorite garden book at 66 i normally dig a 6ft. square then leave it for a day or 2 to recuperate, there"s always something else to do painting, or mending fences etc.

Thanks everyone, its good to get advice from people who know! it will save me lots of time.