The deep midwinter was traditionally the key time of the year for the determined birder to be rewarded with a fluttering glimpse of one of our most majestic predators.

Out on the frost-stiffened salt marshes and moorland, the slate-grey ghost of a hen harrier would reveal itself briefly to the lucky few belligerently battling the cold.

Birds still drift in from further north and the east to escape the worst of the winter weather playing out elsewhere, but English harriers have all but disappeared.

Their absence marks one of the most worrying environmental failures in recent decades.

Their status is so precarious that RSPB bird of prey officer Jeff Knott believes that one wet spring or a fire at the wrong time of the year could result in hen harriers falling extinct. The bird has only been back in England for about 50 years following extinction in the late 19th century.

A recent RSPB survey found just four breeding pairs left in England, all of these birds confined to a previous stronghold for the species in the Forest of Bowland in Lancashire. Habitat loss, as seemingly with all threatened species, has played its part in the hen harriers’ downfall.

But illegal killing is the major reason why the hen harrier could be absent as a breeding bird from England in as little as five years. Hen harriers breed on moors and upland, which are also the key habitat exploited by the grouse industry.

They prey on voles and pipits, but they will kill and eat red grouse if readily available. As a result, harriers and gamekeepers have been mortal enemies for decades.

To compensate for the alarming decline in the bird’s fortunes, they became protected by law — killing a hen harrier now carries a fine of up to £5,000 or six months in prison.

Yet the hen harrier still boasts the dubious title of being one of the most persecuted bird of prey in the UK.

The RSPB wants the laws protecting the birds to be strengthened by seeking a move towards vicarious liability (already enshrined in law in Scotland), where landowners can be held accountable for crimes committed by staff acting on their behalf.

Not only would the loss of the bird be a tragedy for our landscape but it would also represent a huge embarrassment for the coalition, explains Knott, who adds: “Quite apart from the almost unbelievable situation that our modern society could allow a species to be killed into English extinction, it would also result in the Government failing on its commitment to prevent any human-induced extinctions by 2020.”