Smog has reached alarming levels in many parts of London and South of the UK. That famous London skyline is now all covered up behind a sheet of smog. Experts are saying it's a mix of dust from the Sahara and air pollutants from continental Europe. Emergency services have come under strain because many people are calling the emergency helpline number and school children remaining indoors. From the South, experts are now warning the smog will affect the north too in the coming days - reaching as far as Wales.