EIM66135 | Tax treatment of lorry drivers: subsistence allowances paid to lorry drivers: lorries with sleeper cabs: enquiries
From HM Revenue & Customs · Employment Income Manual
Except in unusual circumstances you should not start enquiries yourself into the rates of subsistence allowance paid by employers to lorry drivers who may have sleeper cabs unless:
a high proportion (for example, 75%) of the employer’s lorries have sleeper cabs and
these are habitually used by drivers.
Avoid making the payment of the full rate of overnight subsistence allowance conditional on a statement by the driver that he or she did not use the cab. Documentary evidence (see EIM66120) must be available to show that an accommodation expense has been incurred.