Bob, thanks again for your time and trouble explaining that, I rather belatedly worked out what my cover actually was last night, and a phone call to my insurers this morning confirmed I don't 'CSL'.
They are now working out what the additional cost will be to provide CSL cover upto the 3.5 mil.
To be honest I had completely overlooked this issue and until reading these threads hadn't realised the difference in 3rd party/ passenger cover, I wasn't made aware in conversation with my insurers when setting up the policy. I guess you live and learn!