Adark and stormy night on the Allt a Mhuilinn track. Above treeline the gusts sent us stumbling, and without the ballast of overnight gear and winter climbing equipment we'd have been tossed about like leaves. We battled on through sleet, the haven of the CIC Hut feeling very far ahead. Beyond a bend in the path, torches lit two huddled climbers. One had been knocked off his feet. With a dislocated shoulder he was getting nowhere but cold. I rooted for my group shelter, then we hunkered down to await the rescue team.

I've routinely packed one for years, and though mine sees lots more use on chilly summits with the kids than unfortunate casualties, it's something I wouldn't go without  - especially in winter. Witnessing a recent incident in the Cairngorms only reinforced the message: a group shelter could save your life, or someone else's.  

I often go out alone, and carry a small bothy bag. It's a great asset and I have met a few folk on the hill who have needed it

The over-the-head style shelter is more use than a tighter survival or bivvy bag, easier to accommodate an injured party and with room for two or more people to share heat. Light enough to forget about in your pack, this simple windproof bag might make a critical difference when you need it. 

Mountain rescue veteran David 'Heavy' Whalley is a fan:

"In my early days with RAF Mountain Rescue in 1972 we were lucky to have access to various trades" he recalls.

"Our first group shelters were made by our Safety Equipment Section, sewn from bright orange nylon or old white parachutes. They held about eight team members and were mainly used for breaks on wild winter call outs. Once inside a shelter you were out of the elements and the constant battering wind. You could reappraise the situation and check out how the team members were coping with the conditions."

"We found group shelters were also wonderful for sorting out a casualty" says Heavy "doing first aid, and working out any changes in the search. Thank goodness they became popular in later years as Bothy Bags. A Gore-Tex bivy bag can be excellent but an injured casualty can feel very alone and it's difficult to monitor how they are, especially in wild weather. 

"Every hill party carried a four-person bothy bag which we used on countless occasions, both when training and on rescues. They are brightly coloured for a reason and this visibility is ideal for helicopter evacuation or as a landmark for other team members.

"Today I often go out alone and carry a small bothy bag. It's a great asset and I have met a few folk on the hill who have needed it.

"Warning: If a helicopter is called in be aware that a bothy bag or other loose items will be blown away or worse hit the helicopter. Ensure you pack it away before the cavalry arrive."