AFAICT it won't work like that since no offence would be committed if you moved when directed to do so by the landowner or the police. There is a Government briefing paper at
https://researchbriefings.files.parliament.uk/documents/CBP-9164/CBP-9164.pdf which includes that an offence would only be committed if, "
they fail “as soon as reasonably practicable” to move when directed to by the owner, someone representing them or the police." and I suspect that "as soon as reasonably practicable" will at least give you enough time to become suitably attired and secure the vehicle to travel safely. Also, I could find no provision for fixed penalty fines in the proposed legislation.