SIOG9480 | Settlement by agreement: means to fund the offer: offers recommended for acceptance must always be realistic
From HM Revenue & Customs · Specialist Investigations Operational Guidance
It is wrong to recommend for acceptance any offer or agreement prepared by a taxpayer or adviser that we feel the taxpayer is unable or unlikely to honour.
There is an obligation in means restricted cases to be satisfied that the taxpayer does stand a realistic prospect (not a certainty) of meeting the terms of the offer.