It sounds complicated, but it isn't really to those who are familiar with the matter. Most of it can be done on standard forms and the whole thing can be established in 7 - 10 days. Of course you can sell your flat together with the freehold of the whole house if you want, and the other person's lease would then have to be transferred to the new freeholder. However, this also makes the purchaser of your flat, the freeholder, solely responsible for the building insurance, maintainance of common parts, maintainance of the external parts (foundations, walls, drains, gas, electricity, roof etc) with only the income from the lease to pay for it. You might find that nobody wants such total and sole responsibility and far from it being a benefit you may have to drop your price, That is why I suggested splitting the responsibility of the freehold and selling with a share of the freehold. That way I'm sure that you will be able to increase your price a little. Or of course you can retain the freehold, sell your flat on a lease, and go into the property management business managing the two flats !! But I don't advise it, it can become an awful pain with the potential to lose money.