The fare and Carrier charges can be added together to £ 214.00 which doesn't seem too expensive for the round trip, but adding £123.90 fees and taxes which is 57.9% on top of the combined carrier and fare charge seems excessive.
I suppose the airports have to charge for the use of their services and the maintenance of the airfield just as the carrier has to factor-in the replacement cost of the aircraft as it ages.
If you compare the basic cost of rail travel distances in the UK with the the enormous increase in distance to Canada and back, £337.90 all-in doesn't sound too bad.
Remember, if Ryan Air flew to 'Canada' they would probably fly to Mexico!