While flying today, we kept getting a warning flash up on SD.
It said something like “Warning formation flight up to 3000ft. Active now and for next 50 minutes”,
It pointed to a location about 3-5 miles ahead of our route. We changed direction a couple of times, but it popped up about 5 times, always a similar distance ahead, with the time reducing in real time.
We were above 3000ft so presumably no issue, bur there was nothing notamed in the area.
Is this an error of some sort?

It was definitely a NOTAM.

There were definitely no NOTAMS within the area. None shown on the SD chart and none listed in the NOTAM tab for our route (other than the one noted below)..

I've checked the NATS web sites and there were no relevant NOTAMS.

Sorry, but it was a NOTAM. I don't know what else to say. SkyDemon doesn't just make this stuff up. I'll see if I can find it on our server but it may well have expired.

Thank you.

Tactical NOTAM warnings in flight are always triggered by the outer circle of influence of the NOTAM, not the actual route (in this case) or other more specific geometry which we may have created for a better visual presentation. This is for safety reasons. So it might be you were just touching the edge of a large NOTAM that you had already determined didn't affect your route, because the route described by the NOTAM was actually nowhere near.

Thank you for coming back on this.
I don’t recall such a NOTAM but that may have been it.
I will take note of any further recurrances and check if what you say applies.
Will let you know via this forum, if that’s ok.