Just a couple of tips based on my experience.
1. wear a suit (obvious)
2. put together a business plan and get your sums right. build in allowances such as overruns, re-tests and leasure expences.
3. make sure you own a big pad that you can use as security. The literature says that the loan can be offered unsecured, however, the branches themselves will flatly deny it. I pointed out what the info said and all branches i tried said that it was a mistake. Interesting though, because what with bank rates being what they are, the banks are crying out for borrowers. If they insist on security (which they will) tell them to take a hike. There are cheaper secured loans out there.
4. be with HSBC for at least 3 years beforehand
5. be prepared to be built up then knocked down by nervous business managers who don't know sod all about the industry but who think aviation is not to be invested in.
6. try Nat West. they are a lot more helpful.
7. Don't give up.
8. ...thats it really.
9. The best of british!