http://news.bbc.co.uk/1/hi/uk/6746221.stm Interesting reading... it would been better if they had done the same study using all-white juries as well. Might as well have the complete picture.
you'd also need all female and all male of all the ethnic groups and mixed groups for a complete picture, to remove any bias that gender could create
I would suggest that there have been few, if any, trials where the entire jury was from ethnic minorities, let alone all the same ethnic group. Whereas the majority of cases are overseen by an all-white jury or an almost-all-white jury.
The UK system is a jury picked at random from the electoral roll; that's bound to give a white majority in most cases. Even in Bradford MDC, whites make up 80% of the adult population. If summoned, you are legally required to serve unless you are ineligible for, or disqualified from, jury service. Unlike the US system, prosecution and defence can't try to cherry-pick a jury to suit their case. So the area-wide ethnic mix is preserved.
They came to this conclusion using only 27 juries from one courthouse? Doesn't sound like a really concrete study.