This link is fairly easy to understand .
http://www.autoaddicts.co.uk/brexit-...MTJYaX45Cdq5XA
You do not need a Carnet if it is your own registered vehicle ,and any spares can be on a duplicate list .
Under UK law , any vehicle towing with a gross weight over 3500KG needs a Tacho & O licence unless it is private use only .But you must have all of your facts in place before you go as VOSA can be extremely difficult if they think it might be HIRE OR REWARD