The ultra-low emission zone (Ulez) will be expanded across all of Greater London next summer, Sadiq Khan announced on Friday.The mayor’s decision – which he described as one of the most difficult of his political career – comes in the face of mass opposition and means 15 per cent of vehicles registered in the new outer London zone, about 200,000 at present, will be liable for the £12.50-a-day levy.But an estimated five million Londoners will breathe cleaner air, according to City Hall, due to the likely impact of a city-wide zone further accelerating the switch to cleaner vehicles in the suburbs.More than 96 per cent of cars in the existing zone, which extends to the inner boundaries of the North and South Circular Roads, comply with the exhaust emission rules and do not have to pay the 24/7 charge.