Ask an Property Solicitor. Get an Answer ASAP.
I am a solicitor.
What do you wish to ask about this please? Have you contacted the council as per the letter to voice your concerns?
You should contact the council and raise your concerns in confidence, this is why the council has written to you.
There is no point in speculating what your landlord has applied for, if he did not have a HMO licence previously, the council may take enforcement action against him if he committed an offence.
All the best