Creating two titles from single title

General Discussion

I own a large house that was converted some time in the 90's into two flats; first floor and ground floor.
There is a shared lobby area and then separate door entrances into the two flats. They each have their own water, gas, electricity and each has its own Council Tax rating.
The house is registered with Land Registry as a single title.
I paid cash for the property and it was already converted when I bought it in 2012.
The house is Leasehold with approx 900 years left on the lease.
I am considering selling and re-investing into some other property but I have been advised that the single title may be a stumbling block for a buyer.
What do I need to consider if I decide to create two titles?
Thanks