There should be a weight plate fixed to the B-pillar that you should be able to see when the driver's door is open. Take a photo of that to see the maximum axle weights, as it's easier to see the details on a computer screen.
If you've got 235/45R20 tyres, 2.2Bar (32psi) in all four tyres can support over 2,000kg.
Pumping them up to 2.7Bar (39psi) front and 3.2(46psi) rear can support over 2,600kg, (ie. over 1,200kg on the front axle, and over 1,400kg on the rear axle).
If you're not carrying much weight in the back perhaps try 35psi front and 32psi rear. This can support over 1,000kg on the front axle and about 1,100kg on the rear axle, for a total weight of over 2,100kg.
Excessive tyre pressures is sometimes used to improve handling. However, I expect this is more to do with driving flat out around a smooth racetrack, and not day to day driving on the UK's bumpy and potholed filled roads.