Bronze Circle is a similar mixture to Gold Circle, just without the white clover.
White clover is beneficial in many situations - it increases protein and improves palatability and dry matter intake, but it comes with other issues.
In modern agriculture, there has been a loss of many herbicides which are clover safe, so leaving the clover out allows for a larger portfolio of herbicides to be used, with greater efficacy. The removal of Clover means that the ley can be sown later in the season, as soil temperatures will not be as important.
The removal of clover also allows for an additional kilo of perennial ryegrass to be added to the bag, which increases perennial ryegrass seeds/m2 to 107%, over that of a conventional clover mixture.