The case not being discussed till after the hanging.

I asked in another topic why the House of Commons wouldn't discuss the case until after the sentencing had been carried out. In the film they tell the father this, and he collapses. What I still can't follow, was did the House refuse to discuss the case, or was their some rule that said they couldn't, because I thought I read somewhere that no case could be discussed until after sentencing was completed, and someone posted that to discuss a case before sentencing was completed would basically be like discussing something that hadn't officially happened.
I guess my question is, since so many important people in the House were in favor of Derek not being hung, could they not have taken some kind of stand saying something like "If we are wrong then we've hung an innocent person." If we are right about the death sentence then all we've done is wasted time."
Couldn't they have also brought up the fact that not enough information was given during the trial, the fact that Derek's mentality was of an 11 year old and that he wasn't fit to stand trial as an adult.
The father also mentioned near the end of the film that he was writing to the Queen. Did the Queen have any power to help Derek or address the Home Secretary about his decision? Did she ever answer the letter and acknowledge whether there was anything she could do?
I just don't understand how he was hung, with all the support from government officials and the fact that there was evidence of the trial being mishandled and not all information being given to the jury. Plus the jury called for mercy, couldn't that have been brought before the House of Commons?
I did hear the Home Secretary let the death sentence pass because he figured if a mentally challenged boy was hung, it would be a powerful weapon against future death sentences. If thats the case, that answers my question of why the Home Secretary ignored the information he was given and let him hang.

I plan to read Iris's book if I can get a copy, but if anyone who reads this could answer any of my questions or give me a link to where I could get more information regarding my questions, I'd be great full.