In the UK you do not need to repay in the 14 day cool off period, you can do it at any time. There are no penalties, I believe.
Also, the PCP option with as lower deposit as possible is usually the best way, because you can keep some of your funds liquid and often invest that at a higher rate than you'll pay in interest (if you're wise and have a good adviser!)
My agreement is 5.2% APR - money has never been so cheap!
Yes, personal loans are a lower rate - around 3% at the moment - but you will also need to borrow the balloon payment that way - costing you more each month and overall.
Securing against your house is daft - as to borrow in mortgage format will often incur additional fees such as valuations, legal fees etc - and also even if you pay a 1.xx% rate - if you're doing it over 5+ years (often the minimum term for mortgage borrowing) you will pay more in interested because of that term - therefore costing you more. Also if you run in to any kind of difficulty you could lose your home - and one never knows what the future holds! I would advise securing as little as possible against your home!
Credit cards (if managed properly) can be the real winner if your rating allows. If you can get £25k in credit limits on a 0% deal with the card company then it's the most effective way of avoiding interest while your capital can be held in liquid funds and achieve growth elsewhere. Plus you have the benefit of overpaying easily if you have the ability.
You also have the ability to f*** things up the most easily!
It's a shame that cash is not king - but it's clear there are some real viable borrowing options.
Best is to first negotiate with your dealer about 'what if' prices for your car depending on how you pay - and go away to discuss with someone qualified in finance to work out what's best. But then, speaking to someone qualified may cost you an hourly rate so best see if you have anyone in your friends and family circle!