Can a freeholder change or sell the lease without consulting the leaseholder?

I own a Victorian terraced conversion flat on the top floor and have done a loft conversion with the freeholder's consent. 4 years after I had completed the loft conversion, the freeholder created and sold a lease to the airspace above the property to 3rd party without my consent. I am trying to sell my flat but the buyer has said that he will not buy it unless the lease to the airspace if cancelled as it could mean that the lease owner could develop above the property. In reality, there is no way to develop upwards on top of a loft conversion, nor is there any access to the roof without going through my flat. However, the buyers solicitors have said that with the airspace lease in place, I will never be able to sell my flat as it will put off all future buyers. Is it legal for the leaseholder to sell off the airspace above the property without consulting me first?