Guess its this one...
Police Reform and Social Responsibility Act 2011
Police functions that must be the subject of force collaboration provision
(1)The Secretary of State may, by order, require a specified police function to be exercised in relation to—
(a)all police areas, or
(b)all police areas apart from any specified in the order,in accordance with police collaboration provision.
(2)An order under this section may specify whether the specified police function is required to be exercised in relation to the specified police areas in accordance with police collaboration provision contained in—
(a)a single collaboration agreement which relates to all of those police areas, or
(b)a number of collaboration agreements which, between them, relate to all of those police areas.
(3)Provision under subsection (2)(b) need not specify a particular number of collaboration agreements.
(4)A statutory instrument containing an order under this section may not be made unless a draft of the instrument has been laid before, and approved by a resolution of, each House of Parliament.
(5)If, but for this subsection, an instrument containing an order under this section would be treated for the purposes of the standing orders of either House of Parliament as a hybrid instrument, it is to proceed in that House as if it were not a hybrid instrument.
(6)In this section “specified” means specified in an order under this section.”.
(4)Schedule 12 (collaboration agreements) has effect.