Tenants leave without giving notice or paying rent

Access

Hi, this post is in many ways connected to my previous post.
We believe our tenants are going to leave our property very shortly without giving notice, so they won't end their tenancy, while still keeping some of their possessions in our property while they take their time to move to another property, and not paying us rent.
They have secured another rental through dubious means and had gained a tick on their reference check regarding the question 'Do they pay their rent on time' . They did always pay on time until they got the other property, they then stopped, and we see no encouraging signs that position will change.
This leaves us in the vulnerable position of having tenants with keys to our house but not living there, while not paying rent and not allowing us access, without an injunction to gain access we still can't gain access to carry out safety checks, therefore have no insurance. We doubt very much that they will continue with their insurance cover, if in fact they have any cover anyway.
I'm told by the NRLA, we cannot gain access with the keys while they still have possessions in there, even though it is obvious they are not living there.
Any views or help would be appreciated.