Sorry, maybe I’ve missed something - by using cash (and thereby having a higher mortgage amount), you’d effectively be borrowing at 2.6%, but instead you want to borrow at 4.4%.
I have a pcp with Lloyds Car finance. Personally I have found them excellent. Instant decision, instant cash if you want. Residuals are pretty close to manufactuers on finance offers. Check yiur dealer is on their lost.
