Vistaro

Hi All Been out of the game and the country for 20 years and now back, a lots changed!! Would appreciate some guidance on V5 and Insurance, back in the day I had a trade policy for insurance and we just kept hold of the V5 and gave it to the new owner, now it seems I can't even drive the car unless I tell the insurer the Reg first and when I buy do I have to go through some awful process so the government knows it's in the trade while I'm selling it? Thanks