Dog deposits have been made illegal. It’s part of the reason landlords are refusing pets

Some landlords charge extra rent if they agree to pets.

With the RRB coming in there is talk of insurance but I haven’t seen any which would give me any confidence in being able go repair damage.

Landlords are becoming more and more risk averse. That’s why tenants with poor credit, pets, no references are finding things hard.

Mid tenancy the landlord would have to agree and is highly likely to say no. If the tenant doesn’t respect that they risk receiving notice as soon as the landlord is able

Nope pet deposit are not permitted, pet rents are legal though and the landlord can set it to whatever they want. Also pet could breach of contract if your LL doesn’t agree. If the landlord doesn’t own the freehold then the freeholder could have clause not to allow pets.

Has the landlord agreed to the dog? If they they may add a cleaning charge. Ask the landlord don’t hide that you have a dog as it will a lot worse for you.