The idea that one person's extradition will be permitted on the basis that someone else's extradition has gone ahead is complete nonsense. Alan Johnson, as the then Home Secretary really should know better (but then he is an ex-postie so you can't expect him to have the mental facilties to get his head around the issues).
The point about our justice system is that each case is considered on it's own merits without resort to influence by other cases. This is why in both civil and criminal court cases, information pertaining to other cases, previous cases regarding the defendants is not permitted to be disclosed before or during the main court case before judgement/conviction is made.
You can't authorise an extradition because someone else was or wasn't refused it!
You have to look at the details of the case concerned and judge that.
If however, if the law is not clear, then it might be the case that the particular issue has been clarified by a previous case and a precedent set.
That precedent can then be used to determine the outcome of the later separate case.
For Mr. Johnson not to understand this basic concept in his position of home secretary shows how unfit for office he was.
I shudder to think now what he would have been like as Prime Minister. Perhaps they should set a minimum IQ of 120 for the post! Not unreasonable, I think. Do you really want someone with an average IQ running a country of 60 million people?