I'm assuming by drugs you mean weed as you mention smoking. Unless they're growing/selling it from the property, it's unlikely the police will be particularly bothered about a few people getting stoned at home. Respectfully, they have better things to do than issuing slaps on the wrist (which unless your neighbors have bin bags full of the stuff, is realistically the only outcome here) for personal use.
If they were to act, the first offence is a warning and confiscation, then fines. They can arrest repeat offenders, but it's incredibly rare without aggravating factors.
It may also be the case that they have a medical marijuana prescription, which are now very easy to get.
I'm not sure why you're particularly worried about them smoking in the house... obviously the smell isn't ideal if it's getting into your property but they're hardly causing trouble while indoors.
Noise is a council issue, you should record it and note the date/time as often as possible.
You mention drug deals, it's likely that your reports will be added to the intelligence on the dealers in the area. Again though, in terms of acting on your reports, 1 - it's unlikely they contain actual evidence of drug deals and 2- they're not going to launch an operation to arrest a single dealer dropping off a personal use amount to a house. If they're parking up and selling out of a car in front of the house (I doubt this is the case), that's different but again, unlikely to be a priority without aggravating factors. Unfortunately glaring at you doesn't cut it. If they're threatening or assaulting people, breaching the peace etc, that's the kind of thing where action would be taken.
It'll likely be of little reassurance to your neighbors, but a dealer dropping off to a house (especially a regular customer) is extremely unlikely to be doing anything else nefarious in the area that would draw attention to them at the time, glares aside!
From the landlord's side, warnings/fines would likely be sufficient proof for them to start the eviction process via section 8. Ground 12 (breach of the tenancy agreement, which will almost certainly mention drugs) or Ground 14 (nuisance/illegal use of the property). This can be useful if the tenants are using marijuana legally, as it will likely still be in breach of the tenancy. Copies of your police reports can also help.
I may be mistaken here but I believe reports of smell alone aren't sufficient, but can be acted up on by the council.