I am a landlord as well as an Airbnb host @Amanda860 and have it in my lease that my tenants are not allowed to sub-let and my lease specifically mentioned short term rentals not being allowed.
Perhaps they don't want lots of short term guests wandering around the private estate, perhaps they are worried about security, specialist insurance etc.
You need to understand there is no benefit for your landlord in allowing you to do this and lots of disadvantages; increased wear and tear, security risks, higher insurance etc etc.
In answer to your question, it really depends on your relationship with the landlord, your status as a tenant (how long have you been there/have you always paid promptly) and whether you will be offering a room in your cottage or looking to rent the whole place out while you stay elsewhere.
Can you tell us more about your situation?