I think that seven years is a fair and appropriate sentence for the crime committed. Acts of terrorism, both domestic and international, need to be deterred as fully and effectively as is possible under the rule of law. A strong sentence like this can serve to lead others away from the same path.
Mohammed Uddin pleaded guilty to the charge of preparing to commit acts of terrorism and according to prosecutors made specific arrangements to get to Syria without detection in order to join the Islamic State (ISIS). As an extremist militant group, ISIS has committed beheadings, has interrupted humanitarian aid to war-torn areas of Syria and Iraq, and has conducted kidnappings and suicide attacks. By pleading guilty, Uddin admitted his support for an organization dedicated to violence, murder, and barbarism. Seven years imprisonment for this support seems to be a fair sentence.
Mohammed Uddin was sentenced to 7 years in prison following an arrest, investigation and trial of his actions against the plot of the transatlantic aircraft. Following this arrest and frozen of his assets in Britain, the investigation showed proof that Mohammed was found guilty of housing materials that could be used to make devices. Although no proof was found in his actions, as an accomplice one must also pay the price. He will be followed much longer after his 7 years in jail.
I don't have a specific number in mind, but I think Uddin's sentence should be a little bit longer. While he says that he came back simply because he didn't like the living conditions and the lack of action, there is absolutely no way to know for a fact that he didn't come back with the intentions of carrying out an act of terrorism.