Labour is facing some of the worst results in local elections in its 120-year history, a leaked party analysis has claimed.
Internal research has warned that Labour could lose control of nine councils, with 315 councillors losing their seats in May's poll.
The document, leaked to the BBC, warns party chiefs that they will lose control of councils including Plymouth, Amber Valley and Harlow.
In a worst-case scenario, the party's trouble in the north of England will continue and it could lose control in more of the areas previously considered the party's heartlands.
Among those councils at risk is Sheffield, held by Labour for most of the last 75 years.
Seats are up for grabs in around 118 English local councils on 7 May
Mr Corbyn's successor as Labour leader will be announced on 4 April.
This gives whoever wins the contest just four weeks to try and turn around the party's struggling fortunes.
All councillors are up for re-election in a number of Labour-controlled councils, including Rotherham, Salford and Bristol.
Voters will also be able to elect a third of councillors in 33 metropolitan boroughs and 51 non-metropolitan district councils.
Only Wirral, where Labour is currently running a minority administration, and Burnley, where Labour is already the largest party in a "hung" council, are listed as possible gains.
A Labour Party spokesperson said: "We recognise the scale of the challenge we face on May 7th and we will be fighting for every vote in the local elections."
