LONDON, Oct. 5 -- Britain's National Health Service (NHS) has become embroiled in a heated political and cultural row after a government-backed education programme briefly published - and then quietly deleted - guidance describing the potential social and economic benefits of first-cousin marriage.

The document, posted on NHS England's Genomics Education Programme website on September 22, noted that cousin marriages can lead to "stronger extended family support systems and economic advantages" while acknowledging higher risks of genetic disorders among children born to related parents.

Health Secretary Wes Streeting condemned the document as "shocking," demanding an apology and calling such unions "high-risk and unsafe."

However, MP Iq...