I thought I had been sleeping too long so I asked a friend living nearby. Same phenomenon.
It quickly returned back to normal within a few minutes.
What happened?
The others on this thread had me convinced this was just how sunsets look in the U.K.
Equatorial sunsets are over pretty quick and there's a very short window in which the light path from the sun passes through a lot more of the atmosphere.
The closer to the poles you move the longer the sunsets and sunrises - above a certain latitude you'll find seasons with days that have no night and others that are all night with no day - for long periods the sun is either low on the horizon or just below it.
This opens the viewer up to more reflection and refraction events where dust in suspension, clouds, create wavelength effects on the light spectrum and other illusions.
You noticed it.
A non trivial number of sundowns are spectacular.
We just aren't in the habit of noticing.
Even less in the habit for sunups.
But the light show happens twice a day.
Good luck.
Polution.
the light you saw was probably lensed / prism split by a cloud way off to the west, you happened to catch the light show in those few moments it slid over your portion of the planet.
First time seeing a sunset in the U.K. And I only just woke up so I was surprised and thought something was wrong with my eyes