Best way to fund a private car purchase?

[SSG1000]

Due to purchase a vehicle for £20k, albeit a private sale.

Was looking to fund via my employer (4% flat on PCP’s) but they only work with dealers or are able refinance existing HP/PCP agreements.

My question, how is the best way to fund the vehicle so I can benefit from my employers low rates?

[SSG1000]

Thanks all. Apologies a typo on my behalf the vehicle is actually £30k.

Therefore most supermarket rates cap out at £25k, unless I’m wrong?