The train can be moved within the confines of the branch by prior arrangement, as required by the various agencies (internal and external, such as the ERU and LFB) who use it for training exercises. It's also available for filming. The train may be utilised in this manner as frequently as required, subject to maintenance requirements, staff availability etc.
If the train needs to be moved on or off the branch this has to be done during engineering hours, by way of a possession, because it involves a lengthy procedure concerning the reversal of the points, and also the signals which control access to and from the branch have been decommissioned.
The train could theoretically be used for excursions subject to any necessary remedial work taking place, relevant paperwork being produced and, of course, it isn't otherwise being used for its primary purpose as above.