I posted because I had googled but, despite all the time I spent on it, it was far from clear & I wanted to confirm my findings - people on the forum often have better or more up to date information for which I have often had cause to be grateful, & would hope to do the same when I can.
CBT: we ended up booking flights through Iceland Air, http://www.icelandair.co.uk/
which cost about £200 each including the bike carriage. These were the cheapest I could find last month, & it helps to be flexible about your dates. I think Mondays & Fridays are the cheapest days to fly, you'll see from the website. Good luck, although I hope you manage to sail & avoid burning as much carbon as us.