DIPPRIV5700 | Goods and services for the use of entitled individuals: purchases in the UK
From HM Revenue & Customs · Diplomatic Privileges Manual
There are no provisions for relief on taxable purchases made in the UK by entitled individuals except for:
the purchase of motor vehicles (for the conditions of entitlement see DIPPRIV6100)
the withdrawal from a UK customs warehouse of alcohol and tobacco products (see DIPPRIV3800 and DIPPRIV3900)
under certain limited entitlements granted by the FCO (see DIPPRIV9200)