Join the LAA. Buy a cheap Permit to fly aircraft. Hangar it on a farm strip £100 per month. Fly the living daylights out of it at 18litres per hour. Maintain it yourself with the oversight of a grown up. Thoroughly enjoy the experience.
When you've had enough, sell it for very little less than you paid for it.
Repeat the above if so inclined.
All legal and above board.
Or.
Rent, charge passengers for taxi flights, people trafficking, drug running etc, to cover the costs and profit, work on word of mouth advertising. Change operational bases regularly to avoid getting caught. Budget the cost of fines or jail time for when you do get caught.
Probably very difficult to repeat whether inclined or not.
Not legal or above board.