IHTM33083 | Loss on sale of land: sales excluded from relief: small changes in value
From HM Revenue & Customs · Inheritance Tax Manual
IHTA84/S191 (2) excludes an interest in land from relief whether the sale results in a loss or gain, if the difference between the value on death and the sale value (IHTM33073) is less than:
£1,000, or
5% of the value on death,
whichever is the lower.
If a claim is made where the loss or gain is below these limits you should tell the taxpayers that no relief is available.