validation.uk-utr
The UTR check method follows HMRC's domain library
(https://github.com/hmrc/domain, referencechecker/ReferenceChecker.scala),
Copyright HM Revenue & Customs, licensed under the Apache License, Version 2.0
(https://www.apache.org/licenses/LICENSE-2.0). This capability implements the
same check in TypeScript, Python and Rust.