Hello and welcome. Assuming that this is a bike that you need to test ride before purchasing I’d get some quotes from several insurance companies, eg Bennett’s, Carole Nash, Hastings and maybe a comparison website like Go Compare. You need the ref. number, and bike details. Armed with the quotes reference numbers go and test ride bike. If you decide to purchase you can phone insurance company and activate the preferred quote immediately. Clearly this doesn’t cover you for the test ride so you need to check that the owner’s insurance covers for this. Or you may have decided to buy it by this point and can proceed as above. Tax you can also do immediately by going to the DVLA website. I don’t know if that can be done on the phone as I’ve never tried but you can check beforehand. Good luck with the purchase.