travel costs
I think that the words my accountant suggested the greedy b's at HMRC refer to was "justifiable" and that I would find it hard to "justify" spending more than a full price, rip off, fare just to be able to fly myself the length of the country. Unless there were some other reasons of course. Other flying friends who do ude their aircraft on business have had matching experience i.e. where there was a suitable scehduled service HMRC have used that to argue and then not bothered where there was not. Trips from Scotland to Croatia being an example of the latter.
In the same vein it is difficult to "justify" claiming the training costs for an IR in order to make said trip safer and or more feasible.
Anyway I am all for getting a much back as possible so go for it when you get the chance.