Airlines will vary slightly but, as a guide, GB Airways schedule their flights to take 3 hours 50 minutes outbound and 3 hours 35 minutes back.
Morocco is in the same time zone as the UK but does not 'put the clocks forward' during the summer months. This means that throughout the winter months (when we're using GMT) there is no time difference beteen the UK and Morocco. From the last Sunday in March (when we put the clocks forward to BST) to the last Sunday in October (when we put them back again), Morocco is one hour behind the UK.
Chris