Brake Light Condensation

Having seen the weather forecast, decided to to give our L&K Estate a through clean and polish yesterday - ended up doing a full valet, including Autoglym resin polish and super gloss.

But.... while working on the back, realised the brake light above the rear window had a heavy build-up of condensation - and I mean heavy. Drops of water were trickling down the inside. Can't see any means of popping the cover (which includes the rear washer nozzle) out, so presume the upper part of the interior trim must be removed.

Any ideas on how this can be done? Or should I just wait for the first annual service in a month or so's time?