First thing to say is that there is a complete guide to making alterations to your leasehold property on the Camden council website. Click on (or touch) “Housing”, click on “I am a leaseholder”, click on “Making improvements to your property”. We made substantial alterations to our flat 15 years ago, but the procedures are still the same. Camden is your landlord and you have to do what they require as a landlord, as written in your lease. Camden is also responsible for building control (this applies to all buildings in the borough). What you want to do (remove a structural wall; install a WC) requires the permission of the landlord, but also requires building permission. You need plans drawn up for everything you want to do. You need a cost estimate for doing the works (building control application fees relate to the cost of works). If you want to remove a load-bearing wall, you may need a structural surveyors report to say that what you intend to do is OK. You make an application to Leaseholder Services for landlords permission (fixed fee). You make an application to Building Control for building permission (fee dependent on works cost). Don’t do anything until you have permission! Last thing, if your lease has a plan of the flat and you intend to change the partitions and walls, you will have to pay the legal costs of changing the lease.