SolvedEIM31835 | Travel expenses: general: scale of expenditure
From HM Revenue & Customs · Employment Income Manual
Sections 337 to 339 ITEPA 2003
The tests that apply to travel expenses relate to the nature of the expense and not to the amount. For that reason the cost of business travel is not usually a factor in deciding whether or not a deduction is due. For example,you should not refuse a deduction for first class rail travel, if that has been incurred, on the basis that the same journey could have been made more cheaply in standard class.
Where the travel arrangements are unusually lavish you should consider whether, on the facts of the case, the expenditure is genuinely attributable to business travel or is, for example, some sort of reward. However, you should not refuse a deduction for the actually incurred cost of a journey, hotel room or meal simply because a less expensive alternative is available.