Thin capitalisation: practical guidance: opening a case: pre-return enquiries - no informal comfort
The only form of pre-return consideration of thin capitalisation issues is through an ATCA application from the borrower or their advisors. This is spelt out clearly at INTM480550
A company which makes an approach to HMRC wanting a degree of comfort about its thin cap position should be advised to pursue that by way of an ATCA application. There is no halfway house.
This does not preclude a reasonable amount of informal discussion with the borrower about the timing and mechanics of the ATCA process, what the timetable for dealing with it might be, how the company might assess the risk, etc, but the question as to whether an application should be made is a judgement call for the potential applicant. Estimates by HMRC as to the likelihood of an enquiry ever taking place in relation to a particular set of transactions may be misleading and cannot be binding.
If the company does not wish to follow the ATCA route, and the transactions merit further scrutiny, then HMRC will consider taking up an enquiry once it has the return for the period in question