This paper presents the results of an investigation into the discourse conditions which license the use of British DO. The study takes its origin in Laura Kertz’s (2008, 2010, 2013) work on antecedent mismatches for verb-phrase ellipsis. Kertz puts forth the argument that the information structure of the clause containing the ellipsis has a significant effect on the acceptability of the ellipsis. More specifically, in cases of antecedent mismatch, the acceptability of the ellipsis is greatly improved whenever the auxiliary verb carries contrastive focus. She thus defines two main types of ellipsis, subject-focus (or argument-focus) ellipsis and auxiliary-focus ellipsis. The diagnostics for distinguishing between the two are three-fold : whether the subject of the ellipsis clause is interpreted as contrastive, whether the subject or the auxiliary of the target clause bears a pitch accent and whether the auxiliary of the target clause is redundant. Based on this hypothesis, Philip Miller’s (2011) empirical study of 122 occurrences of VPE involving auxiliary DO showed that a large majority of such instances involve polarity focus, which can be construed as a sub-type of auxiliary-focus ellipsis. The phenomenon known as "British DO", exemplified in (1), involves the use of non-finite forms of DO and is generally considered a related but distinct linguistic phenomenon. However, it has been suggested in the literature (Pullum & Wilson 1977, Baltin 2012, Thoms & Sailor 2018, inter alia) that British DO might be viewed as a form of VPE. This assumption gains support from the observation that British DO is seldom encountered in other varieties of English, notably in American English, where instances of ellipsis would be expected instead: (1) I said that and I realized that I'd said it and I shouldn’t have done. (BNC, British DO) Compare: I shouldn't have (VPE, AmE) Building on the groundwork laid by Kertz and Miller, this study focuses on 418 occurrences of British DO collected from the Spoken BNC. Each occurrence was carefully analyzed in terms of subject-focus and auxiliary-focus, with special attention paid not only to polarity, but also tense, modality and aspect. The results of the study reveal that over 97% of occurrences of British DO involve auxiliary focus, which is even greater than what Miller found in the case of VPE. However, unlike VPE, modality is determined to be the leading factor licensing British DO, whereas polarity focus is a factor in only 11.3% of occurrences. In light of these findings, I conclude that British DO is indeed a variant of VPE, but that the discourse conditions licensing its use are far more restricted than those governing conventional VPE.