Quick answer

Sometimes, but narrowly: a retention of title clause keeps ownership until payment, yet section 25 of the Sale of Goods Act 1979 can give an employer who pays without notice a good title once there has been a disposition, following title into manufactured goods risks a registrable charge, a supply-and-fix subcontract passes no sale of goods, and permanently fixed items become part of the land

Sometimes, but the protection is narrower than suppliers expect. A retention of title clause keeps ownership with the supplier until payment, but section 25 of the Sale of Goods Act 1979 lets a buyer in possession pass a good title to an employer who pays without notice of the clause, once there has been a delivery under a sale or other disposition; delivery to site under a contract that bars removal without consent is such a disposition, as P4 v Unite held. While goods keep their identity a clause can hold good, and a Romalpa clause can trace the proceeds of an authorised resale, but following title into new manufactured goods risks being treated as a registrable charge, as Clough Mill v Martin shows. In construction, W Hanson v Rapid protected a supplier where the employer had only agreed to sell, not bought, whereas Archivent v Strathclyde gave the employer good title under section 25 once payment was certified. Where a subcontractor supplies and fixes, as in Dawber Williamson v Humberside, there is no sale of goods, the contractor owns nothing to pass on, and the employer may have to pay twice. Once goods are permanently fixed they become part of the land, and insolvency law under the Insolvency Act 1986 restricts repossession.