Is it a criminal offence if someone comes onto your property after you remove their implied rights of access (advance notice was given via email and was acknowledged) or is it a civil matter?
It's purely a civil matter unless the trespasser is also intentionally obstructing, disrupting, or intimidating others from carrying out lawful activities. (It would then become 'aggravated trespass', contrary to Section 68 of the Criminal Justice and Public Order Act 1994).
From past posts it could well be bailiffs regarding TV licence....but Chris does seem to have a lot of legal challenges and issues with organisations so could be something else