An anchor assembly (20, 420) for receiving a fixing member, the assembly (20, 420) comprising: a shell (22, 422) with a substrate engagement surface (24, 424); the shell (22, 422) defining a passage (26, 426) configured to receive the fixing member, the passage (26, 426) extending from a trailing edge end (28, 428) of the shell (22, 422) towards a leading edge end (30, 430) of the shell (22, 422) along an alignment axis, an engagement member (50, 450) and a resilient member (40, 440) located in the passage (26, 426), the resilient member (40, 440) defining a through passage (42, 442) for the fixing member to extend therethrough to engage with the engagement member (50, 450), characterised in that: the engagement between the engagement member (50, 450) and the fixing member being such that the engagement member (50, 450) is configured to travel along the fixing member, the engagement member (50, 450) and the passage (26, 426) being configured so that the engagement member (50, 450) is moveable along the passage (26, 426), the resilient member (40, 440) located between the engagement member (50, 450) and the trailing edge end (28, 428) of the shell (22, 422), the resilient member through passage (42, 442) extending between a first end (44, 444) and a second end (46, 446) of the resilient member (40, 440), the first end (44, 444) located between the second end (46, 446) and the trailing edge end (28, 428) of the shell (22, 422); and the first end (44, 444) of the resilient member (40, 440) being mounted in the passage (26, 426) such that it is fixed relative to the passage (26, 426) and such that the second end (46, 446) of the resilient member (40, 440) is moveable with the engagement member (50, 450), and relative to the first end (44, 444), as the engagement member (50, 450) moves along the passage (26, 426) and travels along the fixing member. a shell (22, 422) with a substrate engagement surface (24, 424); the shell (22, 422) defining a passage (26, 426) configured to receive the fixing member, the passage (26, 426) extending from a trailing edge end (28, 428) of the shell (22, 422) towards a leading edge end (30, 430) of the shell (22, 422) along an alignment axis, an engagement member (50, 450) and a resilient member (40, 440) located in the passage (26, 426), the resilient member (40, 440) defining a through passage (42, 442) for the fixing member to extend therethrough to engage with the engagement member (50, 450), the engagement between the engagement member (50, 450) and the fixing member being such that the engagement member (50, 450) is configured to travel along the fixing member, the engagement member (50, 450) and the passage (26, 426) being configured so that the engagement member (50, 450) is moveable along the passage (26, 426), the resilient member (40, 440) located between the engagement member (50, 450) and the trailing edge end (28, 428) of the shell (22, 422), the resilient member through passage (42, 442) extending between a first end (44, 444) and a second end (46, 446) of the resilient member (40, 440), the first end (44, 444) located between the second end (46, 446) and the trailing edge end (28, 428) of the shell (22, 422); and the first end (44, 444) of the resilient member (40, 440) being mounted in the passage (26, 426) such that it is fixed relative to the passage (26, 426) and such that the second end (46, 446) of the resilient member (40, 440) is moveable with the engagement member (50, 450), and relative to the first end (44, 444), as the engagement member (50, 450) moves along the passage (26, 426) and travels along the fixing member.