We have bought tickets from Berlin to Chicago.The flight is BA 8490 ,on the 4th of July,but transit is through London. We have to change the airport during 4 hours. We are from Ukraine and we don't have British Visa. We want to ask if we don't have any problems . According to British Law we can stay transit in Britain during 24 hours without British Visa. We need only 4 hours to move from London City to Heathrow Airport. Will we have any problems with british Visa?