74 Umfreville

I returned from holiday to a letter from Haringey council, saying that the owners of 74 Umfreville Road want planning permission to "retain the existing dormer" at the rear of the property.
This house is clearly an HMO, and the so-called dormer is actually a whole roof extension creating another dwelling space, which was roughly thrown up in a few weeks last year.
Patrick Stewart of the planning office already investigated it and ruled it illegal, now the owner is trying to gain retrospective permission so that he can get away with it.
We have until September 11th to contest the planning application and even then, they can appeal. This just seems to be a charter for rogue landlord to do whatever they like with the houses they own.
Any advice, support welcome, particularly from Umfreville Road residents who should also have received this letter.