Hello I am a solicitor with 20 years experience. I will try to help you with this.
How long is your tenancy for?
we have just signed for another six months from 27th december
Ok so the position here is that on the terms of the tenancy you are not allowed to have a pet. But this contradicts the advertising about the flat. The signed contract will take precedence here so you are not entitled to keep a pet at the flat. However, the landlord would find it hard to gain possession of the flat on the basis had a pet unless a great deal of damage had been done by the dog so although you do not have the right to have a pet the likelihood is that your landlord could not force you not to have a pet if you got one.
But, and this is a big but, if the tenancy ends in 6 months he can get possession of the property without needing to give any reasons when the tenancy ends. So if you got the dog he could wait until the end of the tenancy and then evict you easily.
thankyou for the help. just to make sure that as been a one of payment,as do not want to subscribe to monthly payments,thankyou.