Tom, I'm not too sure re your overall situation here so excuse me
Re the test drive I take it the seller isnt a trader , as if they are then they should have cover for test dives if worth a salt. If its private , do you have a current fully comp policy that covers you to drive other folks cars ( all be it 3rd party only) suely this is adequalte for a sensible test drive. If the seller was worried re you wrecking the car then you coud reasonably put a very large cash deposit in his hand.
If you dont have insurance then there are companies who literally specialise in very temporary cover from one day to one month , they will insure you but but they will rob you blind. Its often cheeper to keep your old fully comp insurance up just so you can use it whilst hunting for your next car.
As for companies only insuring less than x years old or more than y , as mentioed most classic companies will insure anything at all older than 10 or sometimes 15 years old as long as you have two cars. Adrian Flux and Heritage and many others have quoted me so I dont know how you have been that unlucky. Its not your age or location is it ??
R.H keep being mentioned on the forums time and time again as maybe basic but very vry cheep have you tried them. Oh and as Paul says Classic line clearly have a policy that is much more flexible than others and can be a godsend for some
( but not cheap for me).
I have insured a lot of cars because Im always bloomin changing them. I have bought 4 in the last year lol , its got so bad I have been getting quotes for a trader policy purely with a view to saving me money [
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Regards
Mas