If there are no further delays, the concerned rights will automatically be split into a Union right for the EU and a similar right in the United Kingdom. The (split) national English trademark will not be re-examined and no additional taxes will be charged. If rights’ holders don’t want to make use of this, an arrangement to opt-out will be available for this. So no action is required from the side of trademark holders to maintain rights that are already registered in the EU in England.
Also EURID (the registrar that handles the .EU domain names) has announced that it will keep to this transition period. So companies and individuals based in England can continue to use the .eu domain name until December 31.
Things might be different for applications that have not registered yet on the end date. If there are no further delays on December 31th, a extended nine-month period will follow, in which the holders is allowed to convert EU trademark or design applications into a concurrent application in England. An additional fee will probably apply in order to secure these rights.
Many British colleagues have expressed doubts whether the agreed transition period of 11 months is sufficient time to work out everything. Chances of a further delay are therefore not hypothetical. As soon as there is more news about this, we will report back to you.