Libya on the whole is a very moderate Islamic country. Gaddafi deliberately made Islamists the enemy in Libya during his rule. This was so prevalent that people, even after the dictator’s death, are slow to trust the new democratic government in Libya because Gaddafi told the people they were Al Qaeda. As a result the Muslim Brotherhood only won 17 seats in the new Libyan Parliament. William Hague is thus mostly right that the West helping Libya is not the main cause of the war in Mali as on the whole these people are not from Libya. Although I bet that they are using the weapons that the Rebels took from Gaddafi.
These Islamists have been around for ages, at least since the Algerian Civil War in the 90s, but most likely in some form or another for longer than that (see permanent state of war half of Africa has been in since the end colonialism). During the Civil War in Algeria these terrorists were slowly kicked out to Mauretania, Mali and Nigeria (to name but a few countries).
There has been for a long time underlying Islamic Terrorism in North Africa and the recent attack in Algeria and taking over half of Mali has only been able to take place because of misfortunate circumstances (mostly weak governance in Mali). The West have not a lot to do with this. Al Qaeda is mostly interested in taking over countries rather than attacking the West in Africa and we did not unwittingly let forth a flood of terrorists from Libya. I suppose you could argue though that the West is to blame for giving up colonialism in Africa, although I doubt the leftie media are going to argue for a New British Empire. They're not that mad.