Was this itinerary switch valid?

Note: This question is in relation to a slightly complicated scenario outlined here. You don't need to read that question to get a sense of this question.

My wife and I were traveling to India from United States. Our itinerary was as follows:

American Airlines Flight 54 From Chicago (6:00 PM) to Manchester (7:45 AM)
Emirates Airlines Flight 22 From Manchester (8:45 AM) to Dubai (7:45 PM)
Emirates Airlines Flight 524 From Dubai (10:00 PM) to India

I was on a F1 student visa. My wife's situation was the following:

• My wife was on F1 visa which was set to expire by August 2013
• She recently secured a job and subsequently obtained a H1B visa which was valid from October 2013.
• She was carrying the employment letter, visa appointment confirmation letter (proving that she was going to India to obtain her H1B stamping) and the document that stated that her H1B was approved

The agent that we talked to at the Chicago airport for boarding tickets denied us boarding. The reason that the agent stated was that we din't have the proper travel documents -- specifically because my wife did not carry a valid US visa. We explained clearly that the H1B was approved and that we were going to India to get a new visa but he did not accept that explanation.

Even though this was supposed to be a transit flight and the gap between transit was exactly 1 hour, he said that he cannot allow us to board this flight. He kept telling us that there is a chance that we can still get through in UK but that he did not want to take the risk at any cost.

As we were in a hurry, after much discussion, he offered to book another itinerary for us through Doha that does not touch UK.

One of the replies to my original question suggested that I find out if the agent was right in switching our itinerary. However, I am unable to find any concrete evidence. Can someone help me?