Labour must show it can win in key marginal seats when voters go to the polls in May, shadow cabinet minister Jon Ashworth has said.
With "challenging" opinion polls showing Jeremy Corbyn's party trailing the Tories, Mr Ashworth indicated the local elections would represent a key test for Labour.
He said projections by election expert Professor John Curtice that there could be a 12-point swing from Labour to the Conservatives in the contests were "pretty depressing".
Mr Ashworth told BBC One's Sunday Politics: "We have to be winning seats. We cannot be falling back on the scales that have just been suggested."
He added: "Generally, we have got to be winning in Nottinghamshire, Derbyshire, Staffordshire, Lancashire, those types of places, because they contain a lot of the marginal constituencies that decide general elections."
He acknowledged the West Midlands was a "swing region" with some crucial areas.
"We want to make sure that we are turning out a strong Labour vote in Dudley, in Wolverhampton, in Walsall, those sorts of places because they are key constituencies for us in a general election."
Mr Ashworth rejected the arguments made by some on Labour's hard-left that the party should not try to win over Tory voters.
"Some of the debate you see online, on Twitter and so on, suggests that if you want to get people who voted Conservative to switch to Labour, that is somehow a betrayal of our principles," he said.
"It's absolutely not."
Reports in the Sunday Telegraph suggested Labour has built up a £4 million war chest to fight a snap election and Mr Ashworth insisted the party was ready if Theresa May went to the country ahead of the scheduled ballot in 2020.
"We have been on an election footing since Theresa May became Prime Minister," he said.
Mr Ashworth said it was important to accept the result of the EU referendum: "We cannot be like King Canute trying to demand the tide go out.
"We have had this democratic process, we have to accept it."
Former Labour leader Ed Miliband acknowledged the difficult position the referendum had left Labour in, with seats in both staunchly remain and leave areas.
"It's easier for other parties. If you are the Greens or the Liberal Democrats, you are essentially fishing in the 48% pool. If you are Ukip you are fishing in the 52% pool," he told BBC One's Andrew Marr Show.
"Labour needs to try and do something much harder, which is to try and speak for the whole country."
Mr Miliband, who supported Owen Smith in the leadership contest with Mr Corbyn in 2016, said the party had to learn the lessons.
"Why has Jeremy Corbyn won two leadership elections? Because of a sense among party members - but not just among party members - that they felt there needed to be a more radical programme even than I was offering," he said.
"From all wings of the party, you have to learn the lessons of that."
Mr Corbyn will be forced into another reshuffle of his top team after the May elections, as Teresa Pearce is to step down as shadow communities secretary.
She had been filling the post on a temporary basis since October as her predecessor Grahame Morris had been ill.
Shadow local government minister Roberta Blackman-Woods has been tipped as her likely replacement.