When I started my first business the Inland Revenue strongly advised a separate business bank account. However, looking at their current guidance for new business start-ups - available online - HMRC no longer even recommend it.
I still keep separate accounts as I don't want the hassle of separating business from private transactions in one account. To have a joint account with one account holder using it for business as well as private transactions appears to me to be asking for problems.
I suppose I'm just old-fashioned. ;-)