If it's a career development loan that you're after then you don't have to go as far as preparing a business plan. The maximum amount that you can borrow is £8k and that is to a maximum percentage of your course costs (i.e. not 100% but cannot remember the exact figures). Depending on the lender you just fill out a fairly in-depth form providing all your details and the course details and they consider you on that alone. I think that there are about 4-5 lenders currently including Clydesdale, Barclays and others that I can't remember. Speak to one of them and they'll send you a pack that lists all the lenders. I'd give you more info but I'm in the states and don't have it with me.
If you need to borrow more than 8k then you'll have to go to someone like HSBC with a full business plan.
Good luck,
Barnaby