Thank you for your email.
You are correct drones over 2.5KG will have to be registered with the CAA however this does not come into effect until November 2019.
At the moment, it is not possible to register your drone as the system for registering has not been set up yet. Registration should be possible around October 2019.
We have an information service that you can subscribe to called Skywise, this provides information regarding any changes coming about - please click on the following link http://www.caa.co.uk/Our-work/CAA-SkyWise/ if you wish to be kept updated in this area.