Assuming that nothing has changed lately, the E-3Ds are the UK Component of the NATO AEW Force run by the NATO AEW Force Command at SHAPE. Routine day to day tasking is by NATO, with the option for the UK to remove aircraft from NATO Tasking if important national tasking takes priority. (Putting this simply - it can be a little more complicated than that). If the E-3D cannot fulfil its NATO exercise tasking then a NATO E-3A can be tasked in its stead (as, in the past, E-3Ds have replaced E-3As when they have grounded). Hence no operational effect as I assume that no priority National tasking is taking place or being planned at the moment.
I do wish people would know all the facts before they start passing their ill informed opinions......