It is not unusual for a tenant to request the landlord's consent to carry out works to their premises, even though the lease prohibits such works. A landlord may have no objection and be prepared to waive the restriction in the lease. But, what is often overlooked, is the fact that most modern residential leases contain a covenant by the landlord in favour of each tenant in the building, to enforce the tenant covenants in other leases in that building ("the enforcement covenant"). If the landlord waives an absolute covenant in one lease, it opens itself to action by one of the other tenants to enforce that covenant, which the landlord will not now be able to do.
This doesn't just apply to works. For example, if there is an absolute prohibition in a lease preventing the tenant from playing loud music after 11pm, and there is an unruly tenant in the building with a penchant for playing heavy metal music at full volume in the early hours of the mornings. If the enforcement clause exists in the lease, then the other leaseholders would be able to compel the landlord to require the offending tenant to observe its covenant not to play loud music.
However, what if the landlord had previously granted consent to that tenant to play music after 11pm? Would this constitute a breach of the landlord's enforcement covenant? The ruling in Duval v 11-13 Randolph Crescent Ltd  EWCA Civ 2298 has confirmed that, on the basis of the facts, this would be a breach.
However, using my above example, would this still be an issue if the tenant's walls were soundproofed causing no disruption to anyone else in the building?
The article by Hardwicke Chambers uses the metaphor "dog in a manger" to describe a disgruntled leaseholder; conjuring the image of a growling "busy body", with arguably too much time on their hands, who despite not actually being affected by the works "cries wolf" to the Courts with the aim of achieving victory against the landlord for their breach of the enforcement covenant.
Whilst the Randolph case confirms that there is a breach, in relation to any remedy available to the disgruntled tenant, one must start with the question – what is the loss? It is clear from the ruling that the Courts will be reluctant to order any remedy where no such loss has been incurred and are more likely to penalise the "dog in the manger".
However, this is not to say that a landlord is free to waive absolute prohibitions. In my experience of acting for landlords of enfranchised leaseholds, the biggest concern with these types of situations is the precedent that the landlord will be setting in waiving the prohibition. Just because one tenant may have soundproofed walls, doesn’t mean that another tenant will. Therefore careful consideration should be taken in respect of any decision to waive an absolute prohibition; keeping the prospect of a "dog in the manger" situation in mind.
In the words of Lewison LJ, the landlord attempted to paint Dr Duval as adopting a “dog-in-a-manger” attitude. However, that had no bearing on the construction of the lease.