If its for private use you dont have a problem . Hire&Reward your screwed if stopped by Vosa .
It dosent really matter how many seats it says on your V5, Vosa work of seating space , they go by 400mm per person . if your passenger seats total exceeds 8 passengers then its capable of carrying more and you are a psv and as such you need a psv licence , insurance and COIF. dosent matter if you only ever carry 8 or under. I know of many that have been cought out by this and prosecuted . answer is to remove some seats so only 8 can be seated.
If in doubt on any hire&Reward issues join limo chat forum , same as here all very helpfull , but you wont get the answers you want . Many people spending 100,000 of thousands of pounds have tried to do what you are trying and failed . any many still do it illegally though.