US all-purpose flour and UK plain-flour can be substituted for one another without adjustment.UK cornflour is the same as US cornstarch.
UK castor/caster sugar is somewhat finer than US granulated sugar.
There is a product in the US called superfine sugar, which is about the same as UK castor/caster sugar.
Black treacle and blackstrap molasses are similar but not identical.
UK Golden syrup, is the same as US corn syrup.
UK 4oz butter is US "stick" or 1/2 a cup.