UA is still mile based for European addresses. US/AA remains mile based for 2016 as well. By far, DL has the poorest award availability.

If you do not like connecting flights, note that UA has single connection service, MAN-EWR-BNA as does US MAN-EWR-BNA.

Return airfares for mid-January travel approx GBP480 on either carrier on a through ticket.