Can anyone suggest where a Jew and a Christian might have married in England
in the mid-late 1820s?

Mark Levy was >from Plymouth (Devon, England) and Mary Lambert was from
Christchurch (Dorset - then Hampshire, England).
They made their home in the Channel Islands so it's possible they married
there.

Mark retained his Jewishness, so it's extremely unlikely they married in a
church, even supposing it were possible.

Sue Levy
Perth, Australia