Home Office duties in cases of historical trafficking
In Nguyen (Anti-Trafficking Convention: respondent’s duties)  UKUT 170 (IAC) the Upper Tribunal accepts what I had thought was the well established point that the Home Office has duties to historical victims of trafficking:
The duties of a signatory to the Council of Europe Convention on Action against Trafficking in Human Beings include responsibility towards a victim of historic (sic) trafficking into the country from which they later travel (untrafficked) to the signatory state.
See this 2012 Free Movement blog post by David Rhys Jones on Historical Trafficking Cases. However, all this is of no avail to the particular appellant, who loses on the facts of her case.