A salutary lesson - cannabis factory

General Discussion

A note not particularly asking for help but merely on here, hopefully to help others avoid getting into the same problem.
We have rented out a property (my deceased mother's house) for about 12 years with few problems.
The house is a four bed detached in a quiet cul-de-sac.
In May 2018 we took on a polish couple as tenant.
They were (appeared to be) model tenants. They tended the garden; they replaced some old fencing; they filled the window boxes with flowers; they painted some woodwork; they paid their rent on time.
The gentleman had what appeared to be a legitimate business (car repairs). He visited Poland regularly for spare parts.
He asked if he could put some wood laminate flooring down rather than carpet in a television room; we said yes; he did a good job.
He asked if he could put up some wooden horizontal blinds as they would look nice and he can get them for a good price in Poland. We said yes.
His girlfriend left him (he seemed quite sad) but his sister joined him - we checked her immigration status.
We visited the property regularly. Rarely saw his sister she was "in London". He renewed each year through until the present.
We became comfortable with the tenant and reduced our visits. Stupidly, the last proper visit was from our electrician in the summer of 2021. All was fine and the certificate issued.
When it came to the gas safety check and I contacted the tenant to arrange a time for my plumber to visit he said that he could get the man who does the certificate for his business to do it and he would do it for nothing. I accepted and this meant that I did no check of the property.
Some time in the last year the tenant set up his cannabis farm. He bi-passed the electricity meter; they set up high powered UV lights; they hung massive filters and ducting from each bedroom and knocked multiple holes into the loft; they set up three rooms for growing and one for drying. The place is a mess.

I called direct line immediately but we are not covered for "malicious tenant damage" so we have no insurance cover. (It is ironic that our other property insurance does include malicious damage by a tenant).

Learning points

1. - why would a couple want to rent a four bed large detached house?).
2. - cannabis farm operators put up shutters to stop UV light from escaping and alerting the neighbours.
3. - there is a lot of money in this so they can be very patient and lull you into a false sense of security.
4. - do very regular landlord checks - every three months or even more regularly (it takes three months I think to grow a crop).
5. - look very carefully at your landlord insurance. Look in detail at the full policy wording and ask your insurance company.
6. - never be comfortable with a tenant; assume they will do the worst.

The aftermath
We are left with all the factory equipment - the police do not remove this. It is illegal to sell it. We have to skip it although we worry that the rest of the gang will not be too happy with this and others suggest we just leave the house alone for a couple of weeks and will find that all the equipment will disappear one night, then we can start the process of renovation.