The Court of Appeal judgment in Riverside suggested that if rent increases hadn’t been levied pretty much exactly as per any provision in the tenancy agreement, those increases were invalid. Riverside had levied rent increases later than the date specified in the tenancy agreement. This was a rent arrears possession case and the arrears were reduced considerably by this.
It wasn’t something that came up very often – I’ve not seen a case – but was always worth checking, particularly in ground 8 cases.
Now the House of Lords has allowed Riverside’s appeal and largely overturned the Court of Appeal. (Riverside HA v White and another  UKHL 20) .
Although the case turns very much on the specific detail of Riverside’s tenancy agreement, and so it may be possible to make a similar argument on a different tenancy agreement, it is worth noting that Lord Neuberger’s judgment does suggest that social housing landlords, or at least housing charities as in this case, would not be held to the strict construction of the rent review clauses, unlike a commercial lease (See paras 28 and 29).
The discussion of costs at 41 suggests it can be worth thinking about agreeing key questions to be heard as preliminary issues.