Timing of the service of notice on a landlord is tricky. We would never recommend that you serve notice on your landlord until you have exchanged contracts to secure the new property. Until contracts are exchanged there is no guarantee that the new property will be yours. We would suggest you talk to your landlord and warn him that you are looking to move out but without formally serving notice. You may be able to negotiate a shorter notice period with him. To reduce the overlap period in which you would have to pay rent and a mortgage you could agree a longer period between exchange of contracts and the completion date with your seller.