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C. edulis (African) has large yellow flowers while C. chilensis (Chile & possibly a USA native) has almost as large pink-purple flowers but both species hybridize readily creating interbred swarms with chilensis tending to be the maternal parent introgressing its genes with edulis.
Dr Julie Hawkins of Reading University has done dna research on Cornwall carpobrotus populations to ascertain parentage but I can find no results on the WWW. It is very possible other carpobrotus species have added their genes to the mix.
A Google search will supply background.
C. edulis is easily confused with its close relatives, including the more diminutive and less aggressive Carpobrotus chilensis (sea fig), with which it hybridizes readily. C. edulis can, however, be distinguished from most of its relatives by the colour of its flowers. The large (2.5-to-6-inch-diameter (63 to 150 mm)) flowers of C. edulis are yellow or light pink, whereas the smaller, 1.5-to-2.5-inch-diameter (38 to 63 mm) C. chilensis flowers are deep magenta. On the flowers, two of the calyx lobes are longer, extending further than the petals.
The leaves of C. edulis are only very slightly curved and have serrated sides near the tips. 
PS. The light pink is only seen in dying petals.
Many thanks for your comments
From flower colour alone which of course cannot be totally diagnostic, your plant with its particularly beautiful Carpobrotus flowers is the closest to what one expects from a purebred chilensis.
Although some consider chilensis is also native to the USA west coast, no one has yet found evidence of its existence there prior to the arrival of the Spanish Conquistadors who therefore, may have introduced it from Chile.
Regards from downunder.
When browsing through the many Ispot files of misdiagnosed C. edulis. I failed to notice that the plants above were not photographed in the UK. Therefore, they may represent C. acinaciformis or a hybrid with edulis. Both are common in Mediterranean regions and warmer sections of the Atlantic coasts.
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