Be very careful with advice found online, in the UK it is well worth contacting a specialist offshore tax lawyer who will advise you and provide your tax returns usually for around 200 - 300 pounds per year.
The travel days being counted as days in the country is also something to watch out for; the anniversary dates of the tax year and keeping proper evidence. The important thing is to keep boarding pass stubs, passport stamps, crew rosters etc to prove your whereabouts. The IR don't investigate every claim, but a few years down the line you might find you have to prove everything for the current claim and historically.
I use an accountant and simply hand everything over.