Are you absolutely sure about the insurance?
I just did an online quote as a 19y/o male with 1 year ncd, no claims, ?500 excess,social use only, 5k miles based on a PD150 worth ?15k 02 plate. using my postcode
With elephant.co.uk it came to ?3088.68
I'm not disputing your post above but ?1700 does sound cheap for a 19 year old driving a PD150
If I were you I'd get it in writing before I bought the car.