The new owner (ie. the new landlord) will know about your lease because it is a lease greater than 7 years upon grant and your solicitor who acted for you before you took it would have registered it at the land registry.
When the solicitors acting for the new landlord in purchasing the property they would have downloaded evidence of title for the freehold and would see a note against it noting your leasehold interest.
Your rent for the next three years will be governed by the rent set in your lease. The new landlord cannot change it unless the lease terms allow for rent review. You should check. They can only act in accordance with the lease, unilateral rent increases cannot be undertaken by the new landlord so you should read up on your lease as to when the landlord (old or new) can initiate rent review.
If a rent review date has passed and your old landlord did not initiate it then the lease should empower your new landlord to intiate it now. Standard review clauses state that you cannot agree on a figure for the new rent then the matter should be referred to a surveyor to fix the rent at a fair rate.
If you do not have an automatic right to renew you lease at the end of the term then you can only negotiate if you wish to stay there. The landlord is free to ask for whatever amount of rent he chooses, but you are obviously free to accept/reject.
If your lease is not exluded from the landlord and tenant act mentioned above then you will have the right to apply to court for a renewal of the lease and a fair rent will be set during that process.
But, essentially, no - the new landlord cannot up the rent unless the lease allows for it or if there are rent reviews set in the lease which have not occured and even then it would be for you both to agree of in the absence of agreement to be set at a fair rate by a chartered surveyor.
If this is useful please kindly click accept so that I may be rewarded for my time. You will be free to ask follow up questions.