I don't think that the absence of a lease is particularly relevant here. Put it another way, if you had a lease it would have been for 4 years and 9 months and so he would have upped the rent 2 years ago and issued you a new lease.
There is only one question here - Is 25k a fair rent for the premises? If 13k was fair 7 years ago, I would think that rents doubling in 7 years is about right. It's certainly not far off.
Look at it another way, he could have reviewed the rent at any stage over the past 7 years.
I am not a legal expert, but my understanding of the law is that you have a right to a long term tenancy at market rent as you have occupied the premises for more than 5 years. If you can't agree a rent, you can get arbitrators to set it for you.
I think, but I am not sure, that you can say what length of lease you want. In other words, you can opt for a 5 year lease. You do not have to sign a 21 year lease.