Tenant smoking cannabis

Dear Sir or Madam,

I hope all is well.

Our landlord is clearly lying to us regarding smoking cannabis. Neighbors have spotted it several times, some have even gone sniffing the front door and are very frustrated. More than 3 neighbors have confirmed it. As well, this started when the tenant moved in so there is little doubt about it.

We have contacted several times the tenant who says he has never smoked cannabis.

Our tenancy agreement says the below:

Clause 9 Smoking Exclusion The Tenant agrees neither to smoke in or on the premises nor to allow his invited guests or visitors to do so. In breach of this clause to responsible for the reasonable costs or rectification of any damage caused or for any appropriate cleaning, fumigation etc., required

What are we supposed to do in that situation, please?

We fear the property may smell smoke post tenant departure.

Thank you.

Best regards,
Dear Jeffrey,

My apologies, of course. I meant "tenant".

The tenant is leaving in one week after having tried to stay in the flat and pay less than half the original rent.

It is probably too late to evict? So simply let the tenant out?

Nevertheless, we fear that the flat may smell over time.

It is difficult to judge on top of it as each time we bring prospective tenants, the tenant opens all windows..

Should we force some heavy cleaning of the flat? Currently the tenant has planned some regular professional cleaning for the departure but is that enough?

Some residents want to contact the Council regarding this: is it worth it?