Would A's refusal to leave without his vehicle still expose him to a criminal trespass charge?
No. In england-and-wales, this would be considered a civil matter.
Even if tortious liability is established, that alone is not sufficient to constitute a criminal charge. In E&W, criminal trespass is rarely seen in isolation. It usually accompanies a more severe offence. The limited situations where trespass may constitute a criminal offence are if the trespass:
- is aggravated with intent (see s 68 of the Criminal Justice and Public Order Act 1994),
- has taken place in a residential building (see s 144 of the Legal Aid, Sentencing and Punishment of Offenders Act 2012), or
- has taken place on a protected site (eg see s 128 of the Serious Organised Crime and Police Act 2005)
On the facts, none of this has taken place in the scenario you describe. Person A is not liable for aggravated trespass unless he intentionally intimidates, obstructs, or disrupts Person B in doing something they are lawfully permitted to do. Even if this has inadvertently taken place, it is clear that Person A does not have the necessary intent. The second bullet point relates to squatters in residential buildings. That is clearly not what this question is describing. Finally, Person A's land is not a protected site (eg nuclear site or military base) and so the third bullet point will not apply either.