A business plan is your guiding document and is really something you need to do yourself. There are templates available - we got in touch with Business in Focus in Wales but there must be something similar in England, or wherever you are. You need to update it whenever your business changes, and keep referring to it so you know what you're doing. Believe me, your business can and will change and a few months down the line you'll have trouble remembering what your dream was!
Although banks, landlords etc do ask for a business plan it's more than just a thing you have to do, it describes what your business is and how you want it to develop. It's also what wins over prospective investors.
Read "Anyone Can Do it" by Sahar Hashemi who started the Coffee Republic chain. It has guidance on business plans in there and is also an inspirational book.