when i was still in england i was 18 on on my dads green policy which has everything from a jeep to abbot spg on it and i could drive up to my liscence which was his m35 reo (2.5 tons) legaly and i used to buy and sell landy 109s ex military and run them sell them cost me 50 quid to put it on the insurance but because i was on the policy i could drive any of the vehicles at any time as your dad is a farmer he must have like a farmer policy where everything on the farm is covered by one big policy see if you can be added to that as i assume living on a farm you have a tractor liscence so need to use the farm machinery and go that route instead might be worth it