I can see why banks would want you to provide them with a business plan if you were asking them to lend you money. They need to do due diligence and make sure that you have thought about things seriously but...
... I hate business plans, formal ones at least and think other than if you absolutely have to do it because you need to borrow some money, they are a waste of time.
When you're starting your business, of course you need to do some thinking but do not bother filling in a business plan template. There are lots available on the internet but try to avoid them! They are general purpose and make you start thinking about things that may not even be relevant to your business.
The most important question you need to ask yourself, is 'can the business make enough money for me to survive?' For example, let's say you would like to start a taxi company. For simplicity, let's say that you do airport runs to the local airport, at £50 a journey and the journey time is 30 minutes.
You will work eight hours a day, five days a week. Therefore your maximum income will be £100 an hour x eight hours a day x five days a week = £4,000
Not a bad start! Now, you need to subtract your outgoings such as insurance, fuel and taxi licence. For an example, let's say this totals £1,000 a month.
We're down to £3,000 a month. Now subtract tax and some other costs and you're probably looking at closer to £2,000 for what you can take home as salary.
Not bad for a job that you love, being your own boss and having the flexibility that comes with being self employed however don't forget that we are assuming that you will be fully booked, all day every day - unlikely most of the time!
Now think about what happens if you'd like a holiday. Are you making enough money so that you can take four weeks off during the year? Will you need to employ someone to cover you during those periods or will you just shut down the business whilst you're sunning yourself on the beach? You'll need to factor these costs in, too.
That is your basic business plan and something which you can work out pretty easily.
Once you've done the maths and the numbers are looking good, you'll need to think about things a bit more seriously. If the numbers are not looking good at this stage, you'll need to go back to basics. Check what your competitors are charging, are you spending too much on something, are you not working enough hours, is there a gap in the market that you can fill and charge your customers more for?