I have just tried
http://www.airline-network.co.uk/, which we use for comparison costing if Mr Sense is travelling on business. It is only quoting for July next year at latest, and so as school hols (therefore peak period )is from last week of July I entered that and it came back significantly higher. This might be a website to put on your watch list. You can faff about looking at the length of travel time for iceland etc. without spending hours on the phone. Sign up for their fare alert section, hope it helps.
This might be one of those sentences that looks really harsh when written, but it depends how much you value your own time and the ticket flexibility. ( Can you tell Mr Sense once saved a lot of money doing this, but it nearly drove me to the edge of my sanity, we were tired and cross when we arrived on our hols. a great start!) Mr Sense used to work for company who did a lot of airline service work I will try to establish when the schedule is released for next summer! Happy hunting.