Once you have submitted application to swap, your landlord will need to inspect your property to ensure that it is safe and that they are happy with the condition of the property. If you have made alterations to your property these will need to be approved, and the person you are swapping with will need to confirm that they are happy to accept them. Your landlord won’t take on responsibility for the upkeep or maintenance of alterations you have made. Your landlord will also need to book safety tests for the gas and electricity supply.
Your landlord will also exchange tenant references with the landlord of the person you are swapping with. This is to ensure that both landlords are happy to accept the exchange and that neither you, nor your exchange partner has debts outstanding for example.
There are only a limited number of reasons for which a landlord can refuse an exchange application. These are set out in legislation. A good site to refer to for guidance on this is Shelter, but you can also get advice from your landlord or CAB.
If both (all) landlords approve the exchange then you will need to make an appointment with both your current landlord, and your new landlord, to complete the tenancy assignment paperwork granting your tenancy to the person you are swapping with, and accepting their tenancy (or another tenancy in a multi-swap). Do not arrange to move before you have done this.