In cool or moderate British weather I have found the pressure unremarkable in a properly working 900 series cooling system. You should be able to squeeze the large radiator hoses by at least 1/3.
Thoughts about what might cause higher pressure:
- HG failure. Maybe only a very small leak.
- Turbo leaking into cooling system or overheating coolant if water-cooled.
- Faulty or incorrect pressure cap.
- Faulty or incorrect thermostat.
- Incorrect coolant/water mix.
You could try a lower pressure cap (e.g. black) but this isn’t a great solution if you’ve got a genuine fault somewhere.