* PM comes out fighting for aide Cummings
* Adviser accused of flouting lockdown rules
* Condemnation from across political spectrum
* Cummings to make statement in Downing Street
* Police commissioner asks for investigation
* Johnson, Cummings forged close bond over Brexit (Updates with details on planned Cummings statement)
By Estelle Shirbon
LONDON, May 25 (Reuters) - Prime Minister Boris Johnson's closest adviser will make a public statement on Monday after coming under pressure to quit over accusations that he flouted the coronavirus lockdown by driving 250 miles from London to northern England.
Dominic Cummings was facing criticism from lawmakers, bishops, scientists, doctors and police officers who said his apparent disregard for the rules imposed on everyone else had undermined efforts to control the coronavirus outbreak.
Johnson has defended his most powerful aide, who helped him to power and to secure Britain's exit from the European Union, saying on Sunday that Cummings had acted "responsibly and legally and with integrity".
But his intervention backfired, with a growing chorus of critics questioning his own judgment, lawmakers from his Conservative Party publicly defying him by calling for Cummings to go over the 400-km (250-mile) journey, and usually supportive media turning on him.
"What planet are they on?" asked a front-page headline in the Daily Mail, an influential right-wing paper.
With a death toll of around 43,000, Britain is the worst-hit country in Europe and the government was already under pressure over its handling of the pandemic.
Johnson's 10 Downing Street office said Cummings, 48, would make a public statement and take questions from reporters at 4 p.m. (1500 GMT).
Underscoring Cummings' importance to Johnson, he was due to make his statement in the Downing Street Rose Garden, a prestigious venue rarely seen by the public. It was where former Prime Minister David Cameron and his deputy Nick Clegg first appeared together after agreeing a coalition in 2010.
Downing Street said Cummings made the journey to his parents' property in County Durham in late March to ensure his four-year-old son could be properly cared for by relatives if he fell ill along with his wife, who had symptoms of COVID-19.
At the time, strict lockdown rules were in place. Everyone was asked to stay at home except for essential reasons, and those displaying symptoms of the virus were required to strictly self-isolate at home, without going outside at all.
The acting Durham police commissioner, Steve White, said he had asked the area's chief constable to "establish the facts concerning any potential breach of the law" and said the case was "a major issue of public interest and trust".
News of Cummings' trip and his refusal to respond to detailed questions about it infuriated many Britons who had complied with the regulations under tragic circumstances, for example by staying away from dying loved-ones and from funerals.
John Wilson, a man who lost his wife Pauline to COVID-19 in March and was unable to be with her in hospital, spoke of his "rage" at Johnson in a letter to his local lawmaker which he posted on Twitter.
"I would like to know what, if anything, you intend to do about this," Wilson said in the letter.
Scientists and lawmakers said the furore would make it harder to ensure the public kept complying with official social distancing guidance.
About 20 Conservative lawmakers said Cummings should quit or be sacked. They and others reported being inundated with mail from constituents who felt there was one rule for people close to Johnson and another for everyone else.
"It is thus important that Dominic Cummings should now stand down," said lawmaker Peter Aldous on Twitter.
In an unusual outpouring, more than a dozen Church of England bishops publicly condemned Johnson and Cummings.
"The PM's risible defence of Cummings is an insult to all those who have made such sacrifices to ensure the safety of others," said Johne Inge, the bishop of Worcester, on Twitter.
(Reporting by Estelle Shirbon; Editing by Andrew Cawthorne, Peter Graff and Timothy Heritage)
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