Everyone has their own views on security and at the end of the day you've got to make a judgement call on the level of the risk in any given transaction.
I bought a Z last month for £11.5k. The seller suggested I bring cash but frankly the sight of that much money would put me off buying it, let alone any concern as to robbery.
So I went to the viewing on a Sunday with the intention of agreeing a purchase, sending a deposit via internet banking later that day and meeting at a bank to transfer the funds later that week.
Once we'd done the test drive and agreed the sale I thought it was worth trying to complete there and then to avoid a second trip.
Lloyds will let you pay out more than £10k in a day by internet banking.
I put £500 through to confirm that it would go via faster bacs on a Sunday. Lloyds called me for a fraud check (what was the name of your first girlfiend's aunt's dog and all that...) and then the funds went through immediately.
I then put two payments of £5.5k through to make up the balance.
Harder part was sorting insurance over the phone despite having had a quote earlier in the week

some issue with insurance companies not recognising the fact that you might just want to keep your old car for a short time and insure it at a reasonable rate...
Don't get a transporter, just enjoy the drive home it's the best bit!