51Secondly, where the consideration of those elements leads to the conclusion that the transaction in question represents a purely artificial arrangement without any underlying commercial justification, the principle of proportionality requires that the refusal of the right to a deduction should be limited to the proportion of that interest which exceeds what would have been agreed had the relationship between the parties been one at arm’s length (judgment of 13 March 2007, Test Claimants in the Thin Cap Group Litigation, C‑524/04, EU:C:2007:161, paragraph 83).