It would depend entirely on the nature of the "Road" rather than the fact that it falls under private responsibility for repair.
A Private Car Park for example, can fall under the legal definition of a "Road" - where there is implicit or explicit permission for the public to pass - caselaw has defined what is considered a road for the purposes of different legislation.
By way of example, there is no requirement to display a tax disc in a private car park, but a driver could be prosecuted for causing death by dangerous driving in the same place.
If there is implicit permission for the public at large to use the land to pass and re-pass, perhaps as a shortcut for example, I would have thought that the following offence (from the Road Traffic Act 1991) would apply;
6
Causing danger to road-users .Before section 23 of the Road Traffic Act 1988 there shall be inserted—
“22A
Causing danger to road-users .(1)
A person is guilty of an offence if he intentionally and without lawful authority or reasonable cause— .
(a)
causes anything to be on or over a road, or .
(b)
interferes with a motor vehicle, trailer or cycle, or .
(c)
interferes (directly or indirectly) with traffic equipment, .
in such circumstances that it would be obvious to a reasonable person that to do so would be dangerous.
(2)
In subsection (1) above “dangerous” refers to danger either of injury to any person while on or near a road, or of serious damage to property on or near a road; and in determining for the purposes of that subsection what would be obvious to a reasonable person in a particular case, regard shall be had not only to the circumstances of which he could be expected to be aware but also to any circumstances shown to have been within the knowledge of the accused. .
(3)
In subsection (1) above “traffic equipment” means— .
(a)
anything lawfully placed on or near a road by a highway authority; .
(b)
a traffic sign lawfully placed on or near a road by a person other than a highway authority; .
(c)
any fence, barrier or light lawfully placed on or near a road— .
(i)
in pursuance of section 174 of the [1980 c. 66.] Highways Act 1980, section 8 of the [1950 c. 39.] Public Utilities Street Works [1991 c. 22.] Act 1950 or section 65 of the New Roads and Street Works Act 1991 (which provide for guarding, lighting and signing in streets where works are undertaken), or .
(ii)
by a constable or a person acting under the instructions (whether general or specific) of a chief officer of police. .
(4)
For the purposes of subsection (3) above anything placed on or near a road shall unless the contrary is proved be deemed to have been lawfully placed there. .
(5)
In this section “road” does not include a footpath or bridleway. .
(6)
This section does not extend to Scotland.”
Note, that removing traffic cones as a drunken jape might also fall under this offence...
If the road does not have the implicit permission for all and sundry to pass and re-pass, there are far fewer (motoring) criminal offences that the persons responsible are liable for.
