ON A clear day there are few finer roads than the B6318 which runs alongside Hadrian’s Wall. Known as the Military Road as it crosses the roof of Northumberland, passing through some of England’s most beautiful and spectacular countryside.

This particular day in August is neither clear nor conducive to enjoyable driving, however. The rain is coming down in torrents, and the B road with its dips and blind summits is running with water.

Somewhere nestling in the grey landscape is Hadrian’s Wall and Housesteads Roman Fort where National Trust ranger James Howard has been safeguarding a calvatia gigantea, or giant puffball.

He has been keeping it safe for wild food expert Rob Caton, who is heading up a foraging expedition.

But with the weather having taken a turn for the worse (the driving rain is now coming down in monsoon proportions), the small group sheltering in the Housesteads’ gift shop is hoping the expedition can be abandoned and the giant puffball located by more direct means.

James shuffles in looking dejected. “I've some bad news folks,” he says. “The puffball is no more.”

Despite his efforts, it appears some uncaring walker has been unable to resist the urge to kick it. And who can blame them? Who hasn’t delighted in booting a puffball and watching it burst?

Except the giant puffball, which can reach up to 80cm in diameter, won’t have provided any explosive fun. It’s the smaller puffballs that blow up spectacularly.

It seems there are no other giant puffballs lurking along this section of the Roman wall. So plan B is put into operation. In convoy, the party, led by Rob of Byrness-based outdoor adventure provider Wildharmony, heads for the National Trust-run Allen Banks and Staward Gorge instead.

A 10-minute drive away, there is no guarantee of giant puffball success here. But National Trust ranger Laura Jackson has remembered where she spotted some of the round, white fungi last year.

The cars are parked up in a lay-by about a mile from Allen Banks entrance and the group, which includes Rob’s son, Zach, three, marches off across a sheep-filled field towards the far woods.

Running ahead towards a stand of trees, Zach suddenly shouts, “What’s that daddy?” It is a giant puffball, slightly nibbled, but for all that, a fine roundish specimen about 12cm across. Rob slices it open. “If it’s going yellow or brown on the inside then forget it,” he intones. “That means it’s starting to go toxic and you mustn’t eat it. Thankfully, this one’s fine,” he adds, holding up a dense and brilliantly white slice.

There is a collective sigh of relief.

The group sets up camp by the Victorian boating lake under the shelter of the trees. Allen Banks with its spectacular gorge and river is the largest area of ancient woodland in Northumberland, with miles of way-marked walks to explore and abundant wildlife.

Two of the properties’ permanent inhabitants soon make themselves known. The sound of terrified squealing fills the air and suddenly a pair of fighting stoats spill out on to the path.

Everyone watches entranced as they bite and cuff each other before one breaks away and runs off into the undergrowth, pursued by his foe. It lifts the mood, which lightens once again as the smell of frying fungi fills the damp air.

Rob doesn’t believe in over- complicating food. “All you need is a little olive oil and salt and pepper,” he says. “You want to taste what you’re eating.”

He declares giant puffball to be his favourite fungi and says he found one the other year that was so large he feasted on it for a week “morning, noon and night.”