Mini - re "do you think that if the Quran is the spoken word of God?"
I don't believe in God, so no, don't think Quran is the spoken word of God.
"... would it follow then that the Quran is the third book of the bible? "
... but if I believed in God, then yes, I'd say Quran would be the third book of the Bible.
There is huge overlap between the Quran and the Bible, and the God of Quran is very clear that it is the same God who previously sent Judaism and Christianity. Biblical characters appear often in the Quran, with almost identical stories. There is an entire chapter in the Quran dedicated to Mary, mother of Jesus Christ, talking about what a wonderful woman she is.
Don't ask me to quote verses, but Quran is pretty clear that Islam was sent because Christianity went astray, just like Christianity was sent because Judaism got diverted from the path God intended. Iirc correctly, God's main problems with Christianity were the Church & veneration of Jesus, and this is the reason that:
(1) Quran says all you need to understand & worship God is the Quran. No organisation like the Christian Church is needed. No priests etc to show you the way. It's between you and God.
(2) Quran is very clear that Mohammad is the messenger, and although a pretty good guy, not divine.
(3) Muslims are forbidden to draw or otherwise depict Mohammad (so that they can't make icons, paintings, and sculptures of him and worship him)
(4) It is forbidden to change even a letter of the Quran (presumably, so that the message can't be distorted like it was with God's previous efforts at communication)
Having read the Quran as well as the Bible, I have to say that Quran is slightly more reasonable. It features the occasional wife slapping and enemy slaying but at least doesn't call "righteous" a father who offers his virgin daughters for gang rape to an army.
"I had never thought that perhaps Islam is going through a similar process... could it be related to wealth of the nation/culture/people in terms of economic wealth and education, social power at the level of nations but also at an individual level. We like to think that everyone in the UK has equal rights and opportunities but its clearly not really the case."
I think of a religion as a living entity with a predictable life span that includes a Dark Ages period of extremist devotion at the expense of the real world, a fundamentalist (literal) reading of its scriptures, and a desire of its devotees to commit violence on behalf of their religion. Then comes bloodshed and lots of misery. And then through this struggle is born Enlightenment, where people decide to live and let live, everyone's religion to themselves etc.
Science, technology, and pursuit of all things material suffers during these Dark Ages, so it is not surprising that people are left poor and ignorant. You might invent a great new technology but if it's going to upset the mullahs and lead to your beheading, you won't come out with it. Or you may have discovered how the solar system works but if it's going to cause the Church to burn you at the stake, you will shut up about it. It is not surprising that Enlightenment is followed by increased education & wealth, but I don't think that these Dark Ages are caused by their lack.