The Disability Discrimination Act itself does not specify what should be done to make premises accessible, it merely offers a code of practice to do what is reasonable.
To say a wheelchair lift is DDA compliant is a misnomer: you cannot comply with the Act. There are however a number of standards and regulations with which you do need to comply with.
In complying with these regulations it is possible to provide level access solutions that meet with the recommendations of the Act.
In the event that these standards and regulations make the installation of wheelchair access impossible you should be able to demonstrate by way of an Access Statement that you have investigated the provision of level access and that there is no reasonable way of making provision for wheelchair users.