It would help if you told us which platform you're watching it on!
According to Al Jazeera's website, English HD broadcasting is still available on Freeview channel 108 (with SD on 133)
http://www.aljazeera.com/watchaje/
but the Freeview website only mentions channel 133
http://www.freeview.co.uk/whats-on/channels#channels-news
However their detailed channel listing shows that channel 108 (HD) is actually available to approximately 70% of UK viewers:
http://www.freeview.co.uk/wp-content/uploads/2015/06/FV_Channel-Guide-digital_June-2015.pdf
So which Freeview channel are you trying to view it on? (Or are you, in fact, using Freesat channel 203, Sky channel 514, or Virgin Media channel 622? It makes a difference!)