Barrier

1. A collapsible barrier for use as a crash barrier comprising:

a first pair of members pivotally coupled together at a first coupling; and

a second pair of members pivotally coupled together at a second coupling;

wherein each member of the first pair is pivotally coupled at a respective lateral coupling to a corresponding member of the second pair, with the first, second and lateral couplings having parallel pivot axes such that the members are movable from an erected configuration where the members define a free-standing three-dimensional structure with an open-ended chamber therebetween, with the first pair of members mutually inclined at a first angular separation, to a collapsed configuration where the members of the first pair are mutually inclined at a second angular separation which is less than the first angular separation;

wherein the members are biased to move from the erected configuration to the collapsed configuration when one or the other member of the first pair is lifted vertically, with the second coupling moving as far as possible from the first coupling as the members move from the erected configuration to the collapsed configuration; and

wherein at least one part of an attached mechanism is provided at each axial end of the collapsible barrier for joining adjacent collapsible barriers together, end to end, when in the erected configuration.

2. A collapsible barrier according to claim 1 , in which the members are configured as rigid linkages which control the shape of the barrier in both the erected and collapsed configurations.

3. A collapsible barrier according to claim 2 , in which the first angular separation is the maximum angular separation permitted by the second pair of members.

4. A collapsible barrier according to claim 1 , in which the second angular separation is less than 10° .

5. A collapsible barrier according to claim 1 , in which each member of one pair of members is configured to change shape as the collapsible barrier moves between the collapsed and erected configurations.

6. A collapsible barrier according to claim 5 , in which each member of said one pair comprises two parts pivotally coupled together, with pivotal movement of one part relative to the other having a shape changing effect.

7. A collapsible barrier according to claim 1 , further comprising a bracing mechanism for supporting at least one pair of members when the collapsible barrier is in the erected configuration.

8. A collapsible barrier according to claim 7 , in which the bracing mechanism is movable between an active configuration and an inactive configuration, and deploys in sympathy with the collapsible barrier, adopting the active configuration as the collapsible barrier is moved into the erect configuration.

9. A collapsible barrier according to claim 7 , in which the bracing mechanism comprises a pair of linkages pivotally coupled together, with one end of each linkage being pivotally coupled to a respective one of the pair of members supported when the collapsible barrier is in the erected configuration.

10. A collapsible barrier according to claim 9 , in which the bracing mechanism comprises at least one variable length strut, pivotally coupled at one end to the second coupling and at the other end to one of the linkages.

11. A collapsible barrier according to claim 1 , in which the members are panel-form.

12. A collapsible barrier according to claim 1 , in which a part of one member of the second pair extends to one lateral side of its lateral coupling with the corresponding member of the first pair.

13. A collapsible barrier according to claim 1 , in which the at least one part of the attachment mechanism is retractable.

14. A collapsible barrier according to claim 1 in which the at least one part of the attachment mechanism is configured to move relative to the pairs of members of the collapsible barrier in at least one direction to provide a locking action after engagement with an adjacent collapsible barrier.