Nationally, allotment gardening advice is available from organisations such as the Royal Horticultural Society, Garden Organic (formerly the Henry Doubleday Research Association), and the BBCs gardening section.
There are many good gardening magazines, including Kitchen Garden magazine and the BBC Gardeners World magazine. Libraries have a good stock of books on vegetable and fruit gardening. You may also find useful D G Hessayons Expert series of paperbacks which includes the Vegetable Notebook, with charts to record when and where youve planted crops.
On the management side, the Allotments Regeneration Initiative provides a wealth of information presented as factsheets, and the National Society of Allotment and Leisure Gardeners is a useful source of advice to members. Thrive is an excellent resource for people gardening with a disability, while the Federation of City Farms and Community Gardens is a good resource for schools and community groups.