` ` Bongs '' of London 's Big Ben occurs on average for up to six hours . All rights reserved. Clock 's clocks have been shut down for maintenance work . Work being carried out ahead of clock 's 150th anniversary in 2009 . The stoppage will be the longest suspension of Big Ben since 1990 .
` ` Bongs '' of London 's Big Ben occurs on average for up to six hours . Clock 's clocks have been shut down for maintenance work . Work being carried out ahead of clock 's 150th anniversary in 2009 . The stoppage will be the longest suspension of Big Ben since 1990 .