Reported today, apparently a routine inspection of one of the RAF's Battle of Britain Memorial Flight's Merlin engines had a problem show up and they've temporarily grounded all the aeroplanes in the flight which have Merlin engines, so that'd be the Lancaster, some Spits and Hurricanes and presumably not their Griffon-engined Spitfires or their DC-3 or other stuff they have such as the Chipmunks they use for training etc.
Presumably it's nothing major since it's hard to imagine some new fault being discovered on an engine type which has been around in various forms for about 85 years lol. If I had to guess I'd say it may possibly be something to do with using more modern fuel or lubricants in the engines which might cause hitherto unknown issues, but that's just a wild arsed guess. I don't blame them being cautious though, especially since they had an engine fire on that Lancaster not so long ago and it is nearly the only one left in existence which can still fly. Glad I saw that Lancaster flying last weekend because might be stuck on the deck for a while whilst they suss things out.