So long as he had the licence at the time the the property was actually sub-let that would be moot. However, this could be seen as a misleading omission, it really then depends what you wish to do. If you want a reduction of rent, then you will have to negotiate this with the landlord or if that does not get you a remedy you can look at escalating the matter with the housing ombudsman who may be able to assist in obtaining a remedy. However, if you do not wish you live there then you can take the position that they have misrepresented the contract and therefore terminate it without requiring to invoke the termination clauses. What ever route you wish to go down. do not hesitate to act, if you do then the breach of contract can be seen as affirmed meaning you have accepted the breach. The landlord may dispute that it is a breach if that was the case they would require to take the matter to court.
I hope this information proved helpful. You will find a local solicitor who deals with these matters on the law society webpage which is as follows;
Hopefully, I have answered your query in a way that is simple and easy to understand. If anything remains unclear, I will be more than happy to clarify it for you. In the meantime, thank you once again for using our services.
Should you require any further assistance on this matter, please do not hesitate to post a further questions for additional assistance.