buying a house with Absolute free hold but possessory leasehold - implications

Hi,
I'm in the process of buying a house that has both Freehold title (Absolute title) and Leasehold title (classified as Possessory Title), both under the seller's name. I'm curious to know if this arrangement is common and what potential implications it might have in the future. Specifically, I'm concerned about any effects on reselling the house, remortgaging, or any other related matters.
How can these two titles be merged before or after I buy the house?
The leasehold title was registered in 1956 with 200 years lease, and now by current owner. Both Absolute Freehold and Leasehold with possessory title are registered in current owner name.

Any insights or experiences you can share would be greatly appreciated.

Kind regards,

Hi Ashfaque - very much Qs for your conveyancer to answer with regards the affect it might have now and in the future. 
Possessory titles can be upgraded, often after a period of time 
Our Practice Guide explains more re determination of a lease on merger
You won;t get others on this forum sharing their experiences re similar issues. Such a scenario is fairly rare but it's even rarer for this forum to operate like others where the public also chip in with commentary.
Please do discuss with your conveyancer and heed their legal advice

Good morning, Adam,

Thank you for your prompt response. My solicitor explained that with freehold title, the ownership is absolute, making you the legal owner. However, she later mentioned that with leasehold title, the ownership is possessory, which means a third party could potentially claim ownership. I find this confusing because I'm considered both a legal owner (with absolute freehold) and not a legal owner (with leasehold possessory title) at the same time. How is it possible to hold two conflicting statuses simultaneously? I would greatly appreciate your help in clearing up this confusion.

Additionally, I've learned that the upgrade process can take up to 12 years. In regards to the leasehold title, the current owner possesses a copy of the old leasehold deeds but not the original. Would providing these documents potentially upgrade the possessory title to Good Title? I eagerly await your insightful response.

Best regards, Ash

G M Ashfaque - clearing up any confusion is very much for your legal adviser to help with as explained.
Freehold and Leasehold are two different types of tenure so it is not unusual to have both re a single property and for the class of title to then differ. They key Q for you would appear to be whether the seller owns both and what impact having two separate tenures then has on you as a buyer/owner - very much for your solicitor to answer. 
The PG I linked to explains how a possessory title can be upgraded and we would not offer a view beyond that guidance without an actual application being submitted. So once again the Q is one for your solicitor to answer for you.