I would say it is not allowable for two main reasons:
Firstly, having been involved with your previous posts, the information provided suggested that there may well be duality of purpose in your trip(s) abroad. If dual purpose expenditure cannot be logically apportioned, then the strict statutory position prevails i.e. that the expenditure is not allowable.
Secondly, even if it is claimed that it is for business use only, in practice a non-business element must exist. The passport could in the future be used for personal travel. It can also be used as an identification document.
And finally, even if it was allowable, there is a logical argument that the cost of the passport £77.50 should be spread over ten tax years since it has a ten year life. Remember that the effect of deductions is that you don't literally get the money back from HMRC - you get tax relief at your highest rate of tax. So assuming 20% liability the relief in terms of "money in your pocket" would be £7.75 @ 20% = £1.55 per year.
I cannot believe that I have gone into so much detail over something with a potential tax saving of £15.50!
