Why the UK sticker uses PSI while the continent uses bar

UK vehicle handbooks and door-jamb stickers almost always give tyre pressure in PSI, whereas most continental European manufacturers print bar figures, even on cars sold in the UK through the same European group. If you are checking a pressure figure from a European forum or manual against a UK pump gauge, always confirm which unit is printed before adjusting, since 2.3 (bar) and 2.3 (PSI) are wildly different pressures.

Legal minimum tread depth is not a pressure rule, but it is linked

UK law sets a minimum tyre tread depth of 1.6 mm across the central three-quarters of the tyre. Running underinflated tyres accelerates uneven wear at the edges, which can push a tyre below this legal limit faster than normal, in addition to the fuel economy and grip loss that come with low pressure. Both are checked together at an MOT.