I'm still trying to work out for myself what the likely or even possible effects are, so this is a work in progress.
In descending order of certainty...
Common law summary possession by a local authority/public body landlord after Notice to Quit (e.g Ex joint tenants; temporary accommodation under s.183 and possibly s.192 HA 1996; 'successors' to deceased tolerated trespassers; non-successor occupants; etc.)
Possession proceedings will need to include the potential to consider whether the eviction is proportionate under Art 8.2 ECHR.
Does an assertion that the eviction is not proportionate constitute a defence? I think it is likely to be so. Although alternatives might include compensation, if the eviction is disproportionate, the court would be aiding a breach of Art 8.2 in making a possession order. (The similarity to the 'unlawful act' element in Malcolm v Lewisham might mean that the House of Lords judgment in Malcolm has an impact, but Malcolm concerns interpretation of statute, not ECHR).
Where will this leave the tenant? Most likely as an ex-tenant still in occupation. I can't see much in McCann to suggest that the ending of the secure tenancy per se was taken to be disproportionate, the issue being purely that the possession proceedings could not consider proportionality of eviction.
Mandatory possession proceedings brought by a public body landlord under statute - for instance introductory and demoted tenancies.
Trickier, as to some extent the summary nature of the possession hearing is given in statute. While in common law proceedings, the Court can introduce 'proportionality' under its own duty under the Human Rights Act, it is surely different where the process is statutorily limited. Would the best the Court could do be a declaration of incompatibility?
Possession proceedings by non-public bodies, private landlords or RSLs, where summary or mandatory.
There have been suggestions that McCann might hold other than for a public body landlord. Given that private and RSL landlords have no duty to comply with the ECHR under the HRA, there is no duty on them to behave proportionately in evictions and therefore no basis for the court to hold them to proportionality as being their duty.
So, the only way that I can see that McCann would extend beyond public body landlords is if the Courts, as public bodies, are taken as being required to consider proportionality in their decisions to make an possession order - the duty of behaving proportionately being the court's, not the landlords. Thus there would be a general duty to consider proportionality in all possession claims, whether brought by private landlord, RSL, public landlord, and whether summary, mandatory, or discretionary.
I very much doubt that this can be the case. It is not, after all, the court that is evicting the (ex)tenant/occupier, it is the landlord.
McCann focussed on the procedural 'defect' of the summary possession procedure against a local authority (ex)tenant. The LA's ability to 'sidestep' the requirements of HA 1985 via the NTQ was specifically raised as an issue by the ECtHR in the judgment. The ECtHR acknowledges that the existing summary procedure, and the availability of JR, provides safeguards to ensure the possession claim is lawful and for a legitimate purpose. If the ECtHR had been concerned with possession claims in general, then the lack of availability of JR against private or RSL landlords could have been mentioned as an even greater defect. But it wasn't.
The 'procedural defect' is therefore a lack of ability to scrutinise whether the landlord's interference with Art 8 rights is proportionate. This can only be the case where the landlord has a human rights duty to act proportionately.
I would be keen to be shown I was wrong, obviously, but I can't see how McCann can extend beyond public sector landlords. Even if it does, we are back to the issue of statutorily given processes (s.21, mandatory grounds, etc.) and declarations of incompatibility.
Doherty v Birmingham in the Lords will give some clarification, but it is going to be fun in the County Courts for a while.