The Treasury's guidance to staff travelling on official business is that standard class should be used. However, first class travel may be used by staff at all levels where there is a business justification or when travelling at peak or other times when trains are likely to be crowded. In all such cases staff are required to provide an explanation for the use of first class travel when claims are made.
HM Revenue and Customs' policy is that staff travelling by rail should use standard class. However staff at Grade 7 and above may travel first class if certain conditions apply. All staff may upgrade to first class on the day of travel if no standard class seats are available on the rail journey being taken.