Dear companycar
In addition to the good advice given above, I would like to add the following.
If you can get a letter from your employer confirming that you have been driving a company car for 10 years, this will be taken into consideration.
You could also try getting a quote on-line, putting in 10 years (full bonus), with any of the following companies and then phone them to confirm that they will allow the bonus, subject to a letter from your employer. They will then normally allow the preferential on-line price.
Ecar, Esure and their associated companies, Direct Line and their associated companies.
Hope this helps.