Why local democracy is a bad idea

In the UK the government is thinking of handing more power and money to local government, and allowing election of mayors to cities like Manchester.
This may sound like a good idea. Unfortunately turnout and interest in local elections is low. Many councillors are elected unopposed and many local councils have been local one party states for years. Local democracy will mean more corruption and lead to less trust in every sort of public servant, including even police, who now also have oversight by locally elected officials.