Here are some useful sites to peruse if you are thinking of a loft conversion...

Local Authority Building Control

Finding an architect (pdf document from RIBA).

Books on managing loft conversions - from Amazon.

for renowned roof window solutions.

suppliers to the DIY & building trade.

The UK's No.1 independent website for loft converters - with FREE  plans and downloads. At Loft-rooms.com you will find essential information for a successful loft conversion  -  everything from the latest planning and building regs to free span tables, sample drawings and party wall advice. Don't start work without visiting us first! 

Federation of Master Builders - professional body of the building trade, this site has useful info. on finding a builder, contracts with builders and other info.

supplier of space-saving and high-performance thermal and acoustic insulation products

Specialists in loft fittings (windows, stairs, flashes). This link takes you to their frequently asked questions page which explains more about trussed lofts and building regulations.