Tony Blair's name isn't on the ballot but he faces a crucial vote Thursday in local elections widely seen as a referendum on the prime minister and his problems.
Blair has suffered through a rough couple of months and voters could use town and city council elections around England to punish him for a slew of scandals.
They include officials' failure to screen more than 1,000 foreign prisoners for deportation before freeing them, allegations that Blair nominated four financial backers to seats in the House of Lords as a reward, and even the deputy prime minister's extramarital affair.
Voters are choosing representatives to fill 4,360 seats in 176 local authorities and municipal councils across England, a little less than half of all English councils. London is the biggest battleground, with elections in all 32 boroughs.
Polls opened at 0600 GMT and were due to close at 2100 GMT, with results due late in the evening.
Blair and his wife Cherie voted early at Westminster City School, where Conservative candidate Louise Hyams asked for their support.
"Fat chance," Mrs. Blair said.
If Labour candidates fare poorly and the party loses control of councils, it could heighten dissatisfaction with Blair in the party ranks and intensify calls for him to step aside and let his likely successor, Treasury chief Gordon Brown, take over as prime minister.
The string of troubles has left many longtime Labour supporters dispirited and could help the opposition Conservatives and third-party Liberal Democrats snatch seats.
"This is an opportunity to register a protest vote," said north Londoner Steve Harman, who said he votes Labour in national elections but will back the Green Party this time, reports the AP.