UFO Anglia UK

On my way back from work this evening I saw something I didn't recognize.

Above Milton Keynes town center I saw two white lights, no movement at all. I could see a plane higher in the sky approaching that direction, and could see that this object wasn't moving in relation to the plane.

We continued along the road (my colleague driving) and as we passed I had a view from beneath. There was a slow red pulsating light and two bright white lights, all in a perfect triangle shape. It seemed to rotate slightly, but still wasn't travelling in any direction as far as I could tell.
The red light was intermittent. While I could see all three, the red one stopped, then started and pulsated slowly.

We turned a corner and I watched as this thing began to move off in a N/West direction, not fast, I suppose about the speed of a helicopter maybe.
The plane I had matched it with (much higher and I could see the white light with a red flashing light at the back) had by this time passed above my mystery lights.

Then it was out of view.

I watch the skies often, I've seen things before that I couldn't explain, and meteors a few times. Recently I have paid more attention because we have increased media coverage of these things here in the UK at the moment.

I can honestly say that I have never seen an aircraft in our skies with a perfect triangle of three lights, I've never seen an aircraft pause in the sky above here other than a helicopter.

Is this a familiar aircraft?
Is it a familiar UFO?

It should also be noted that in the 1970's while our town was building the largest covered shopping center in Europe (at the time) UFO reports were common above the area. The area directly below this craft I have seen is where considerable construction is going on, Just along the road from the shopping center. New apartment blocks are going up there.

I didn't have my phone with me, so no pics, sorry. But if you like I can try to make a diagram of the town center in association with what I saw.

Any thoughts on this?

Over South wales several weeks ago -the following passed overhead.

Very faint eges of what appeared to be an obtuse triangle shaped plane. very dark or dull. had two rear corner lights,white which I seem to remember pulsing at same time.
no leading(front) light that I remember.
A strange middle rear orange/red light. letterbox shaped that pulsed on&off, had a wait,then on&off..etc.
what was strange was the size speed & sound(no sound).
To appear so slow passing overhead and be quiet ou'd think it was miles above. But it didn't look that high. The lights & size were of something almost low passing-yet it was quite big. seemed&felt really odd!