UK cold weather: what are the health risks and who is most affected?

When temperatures plummet, hospitals receive more patients with heart attacks, strokes and respiratory infections, including influenza. Photograph: Jacob King/PA

With weather forecasters warning of low temperatures and potentially severe overnight frosts across the UK from Wednesday, the UK Health Security Agency is urging people to keep warm and look out for others most at risk from the cold. But what are the dangers that cold weather poses?

How does the cold weather hit health directly?