Re: reasonable person?
>>"Wouldn't that depend entirely on where in England the case took place. I believe there a cities where the "ethnic minorities" are only minorities when compared to the entire country but locally represent a very large part of the society. "
Yes, of course. However, the local areas you're referring to where a minority is in a majority are much smaller than the jury catchment areas for a particular Court. See FOI request: https://www.whatdotheyknow.com/request/crown_court_juror_catchment_area, which shows that the jury catchment areas for each court are gigantic and take up several postcodes.
Add to that the fact that in order to serve on a jury you need to be both registered to vote and resident for UK for at least five years- both of these things further dilute any influence that a majority-minority area might have on jury selection.
The odds of finding your 12 religious conservatives on a jury appear to be so small as to be not worth worrying about. Of course, that's not going to stop the Express etc from worrying about it, it just stops the worrying from having a rational basis in the absence of any compelling evidence to the contrary.