For full business use declaring 40K business miles including cold calling (sales rep) 10 K personal I got mine done to 480 with swift.
If you do use your car for work (other than go to and from place of work) well worth declaring as insurers will not pay out.
I have full no claims and 1 no fault accident (3rd party paid out) I thought was very good.
Swift cover is basic so added a extra 30 quid for repalcement car and legal cover.
However if I had insured the ZTT with Peter Best Insurance on classic policey it was silly cheap no no claims is needed 100 excess free screen cover and agreed value.
My wifes Zr was 260 for 05 agreed at 4K but down side is 5000 miles a year.
Having seen the amount of Zeds being writted off for minor (cracked bumpers) I would strongly advise gap insurance if your car is on finace as you will be horrified what the trade value the cars at.
The flip side is that you can buy very cheap cat d cars pay 200 quid to body shop to fix cracked bumper and have a really cheap car. Worse case is that if it is written off most will reduce payout by 10%, but then is you have saved over 50% on forecourt price got to be a no brainer in my book.
Thats why so many do it
I hope that helps
Peter