Doesnt matter if its a main road or not, its still a public road. Ive had to boot the old mans BMW off the drive to make room for my MK5 as its only insured to be left overnight on the drive way.
As jv says, despite not having NCB you have 18years driving and thats sounds REALLY high. I had mine insured last year for just over £1k when I was 22 with 1NCB and living in Croydon, that was with Greenlight.
Mine isnt a million miles off what that quote is and thats now with a DR10 so I think you can find it for much cheaper than that.