So I was working on Soviet Invasion of Iran, and one thing I'm trying not to do is make any large extrapolations on what changes the story's happenings will make to the future.
But one thing I kind of thought about was the fact that the Shir Iran, the tank that was ordered by the Shah but would be sold to Jordan as the Khalid, was to be followed by the Shir 2. The Shir 2 was a qualitative leap from the Shir Iran, which was itself a step from the Chieftain.
When the Iranian Revolution happened, the Shir 2 was diverted into service with the British Army and given a few extra bells and whistles, namely Chobham armour and became the Challenger 1.
Now, had the Shah stayed in power long enough to complete the sale, or had Parliament decided to just cancel the order entirely, then the British Army would have had to wait until the tank that we know as the Challenger 2 before it could replace the Chieftain.
In Desert Storm, they took the Challenger 1 into battle, but under these changed circumstances, the UK 1st Armoured Division would be going into battle with the Chieftain.
It's not a huge change, but by that point, the Chieftain's transmission issues had been largely worked out. The tank has a stained history. Ending it's career with a big win in the nougaty center of Arabia might be just the thing it deserves.