This section applies to the construction of a provision which—
does not confer power to detain a person, but
refers (in any terms) to a person who is liable to detention under a provision of the Immigration Acts.
The reference shall be taken to include a person if the only reason why he cannot be detained under the provision is that—
he cannot presently be removed from the United Kingdom, because of a legal impediment connected with the United Kingdom's obligations under an international agreement,
practical difficulties are impeding or delaying the making of arrangements for his removal from the United Kingdom, or
practical difficulties, or demands on administrative resources, are impeding or delaying the taking of a decision in respect of him.
This section shall be treated as always having had effect.