If you decide to take on the challenge of a seriously overgrown allotment and feel that you need something a little sturdier than a spade to help you to clear the space, then weed killer has a place where a rotovator should not be your first port of call. You do not wish to be cutting up the roots of buttercup, dandelion, dock, couch grass or bind weed into small pieces as each one will regrow into another weed. The end effect will be worse than the problem at the beginning.
Weeds are best killed with systemic weedkillers based on glyphosate applied from mid-spring until mid-autumn. There are a number of such weedkillers available on the market. Most garden centres and stores who stock garden accessories in season can sell you glyphosate based weedkillers in small quantities ready for use either under their own brand name or under a trade name.
Roundup is the most well known trade name closely followed by Resolva. The advantage of buying either of these is that you can obtain them in concentrated form which will be less costly for dealing with a large area of an allotment.
If you have a full 10 rod allotment which is approximately 250-300 square yards or even a half plot at 5 rods which is seriously overgrown then a concentrated weedkiller will be less costly on your pocket than buying one which includes water already added.
If your allotment site has a water supply available then you can mix on site. Otherwise you can obtain a 5 gallon water container fairly easily for carrying water to your allotment (ask on your local freecycle site, see your fellow allotment holders, look on eBay, visit a good camping store or even see if a local cafe has empty containers you could acquire).
Both Roundup Concentrate and Resolva Totalclear Concentrate are available from Amazon if you are unable to find any in your local garden centre. It is worth looking at the prices online before going shopping so that you can make an informed choice as to how your pocket is affected as well as being informed as to the most suitable product for your problem. It should be noted that none of these chemicals affects the soil – they just have a long term effect on the weeds that you spray.
If you are faced with brambles and other woody growth, then you will have to use a different technique and the Royal Horticultural Society covers this in detail, including suitable chemical treatment if required.