Tesco are offering 25% off when you buy 4+ bottles at the moment. This offer works in addition to other offers, so there are some good deals about.
e.g.
www.ispyprices.com/search/q%3D+oyster+bay+merlot
www.ispyprices.com/search/q%3D+wairau
I haven't tried the merlot at the top of the list, but will £3.37 a bottle.
www.ispyprices.com/search/q%3D+merlot
Worth buying a Christmas supply and hoping it will last till then?