Number plates should show your vehicle registration number correctly. You can’t rearrange letters or numbers, or alter them so that they’re hard to read.
If you drive with incorrectly displayed number plates, you could be fined up to £1,000 and your car will fail its MOT test. For more info: https://www.gov.uk/displaying-number-plates/overview.
If stopped by the Police, those with illegal number plates will be issued with a VDRS (Vehicle Defect Rectification Scheme) ticket which requires them to change their plate (in accordance with the law) within 14 days and to get this certified at an MOT testing station/garage.