A short news article on BBC News has announced that aircraft of the Battle of Britain Memorial Flight have been grounded, due to "engine issues".
The aircraft affected are the Lancaster, and the Merlin-engined Spitfires and Hurricanes. Apart from the term "engine issues" with the Merlin engines, no further details are available at present, although it has been suggested that this is a temporary situation, whilst the problems are corrected.
The Dakota and the Griffon-engined Spitfire PR19 are still cleared for flying, along with the two Chipmunks used for training.
Although it's wrong to speculate, I suspect that this is due to some problem with perhaps one engine, possibly with an aniclliary that could be, or is, common to all, and the 'grounding' of all Merlin-engined aircraft is a precaution.
Let's hope the problems are sorted as soon as possible.