Landlord selling house and ground Separately

Can anyone advise please? We rent a house with what we thought was a large garden, (described as garden in the lease). The landlord has now advised us he is selling the house and "building plot". The question is, if the building plot sells before the house, what effect does this have on our lease? Can the land be sold whilst we are still renting? Would we have to have a new contract?

Thanks everyone
Joyce