3 red triangles flying at speed in formation

It was a clear night in the remote town of Kirkcudbright, I was stargazing with a friend (I was 17 years old at the time). I was an aircraft enthusiast and knew what various known craft looks like and flies like.
At around 10.30pm I saw three glowing red/orange triangles (isosceles) travelling west, flying in formation. Two were at the front and one at the back. Height was high, probably jumbo jet altitude - they looked like they might have been slightly bigger than a 747. They were totally silent and no trials. The one at the back suddenly shot forward at lightning speed, no visible acceleration or deceleration, just ‘zip’, and it became the leading craft. The other two, now at the back, then swapped places sideways, again at lightening speed, then back again. There was no sound. I watched them in their new flying formation until they vanished out of sight.
I knew not of any aircraft that could move like that back in 1991, and not even of any now in 2023!
The person I was with also saw them but we never discussed it in detail.