Bit of an odd one to ask here since I'm based out on Dartmoor but did anyone manage to get footage? I've been tracking a very similar triangular formation report from about three weeks back over Wiltshire and the witness described the same slow drift pattern before the lights just went dark all at once, no fade, no scatter, just gone.
What altitude were they moving at roughly, and could you hear anything underneath them? That's the bit that always separates the military TR-3B crowd from the genuinely unexplained stuff in my experience. Silent and low is where it gets interesting.