The Housing laws, my favourites
First of all, letting agents don't have to pass exams and anybody can set themselves up as a letting agent. Many landlords don't seem to have a clue about the housing laws and use letting agents, even though the landlord is the one who is responsible for ensuring thy don't do anything criminal.
What does your contract say? Typically everything requires a professional clean (oven, carpets, curtains, and the house, receipts must be provided or you won't get your deposit back).
Only if the landlord has the proof it was all cleaned by professional cleaners just before they moved in. Landlords cannot have betterment. It's why the deposit schemes were added to the England and Wales Housing Acts, to save the courts being clogged up with tenants' taking their ex bad-landlord to court.
If the contract has all of that, put in writing WITH PHOTOS that you will not be returning the property professional,lay cleaned but instead as you found.
That's already the law in England: the property to be returned in the same state the tenant was given it, less fair wear and tear. You cannot take away someone’s legal rights in a contract. There will be a list somewhere on the internet on what has been ruled as “unfair terms” in a rental contract: meaning they won’t apply.
Did the house have an inspection report when you moved in? More to the point, has it been signed by both parties?
Shelter England are quite good with advice on bad landlords, as is the landlordzone, who have professional landlords on there who are fed up with the "me too buy to let" landlords who haven't got a clue on the legal side of their business. The government have recently brought out a leaflet too to help renters and brought in a nice law change that will hurt the bad landlords.
I did write a few articles for tenants with bad landlords and landlords with bad tenants, a while ago and they will still be around on the internet, but they will be out of date as laws change all the time. I would use the landlordzone for advice if I were you as these professional landlords tend to keep up the date with all latest law changes and high court cases.