IDG30450 | Confidentiality when dealing with the customer: disclosure to agents, representatives and third parties: employment references
From HM Revenue & Customs · Information Disclosure Guide
The department does not make any employment references for our customers. If a customer wants access to any information about themselves, they must make a Subject Access Request (see IDG30220).
Please contact your Security & Information Business Partner (SIBP) if you feel there is any reason why you should provide a reference for a customer.