Labour's PM has come under fire over donations, freebies and the departure of his embattled chief of staff Sue Gray.
But, shrugging off weeks of headline-grabbing rows, he insists: "I don't look backwards, I never have.
"Mirror readers will judge me on my actions.
We're just getting started."
And he promises to deliver "the honesty working people deserve".
Mr Starmer's rallying cry comes a day after he admitted to suffering "choppy days" in the first 100 days of his premiership. But he says he's already started to fix Britain's foundations after 14 years of Tory misrule.
He writes: "Readers should know I'm not interested in slapping a bit of paint here or doing a bodge job there.
Mr Starmer listed a knife crackdown, a long-term NHS plan and teacher and police recruitment among measures already underway.
And with Britain set to host a major investment summit on Monday, Mr Starmer hailed the opportunity for international giants to pump cash into towns and cities - and the launch of Labour's long-promised Modern Industrial Strategy.
He promised thousands of jobs would be created through more than £24billion of investment into the green energy industry.
BY KEIR STARMER
IT'S been 100 days since the nation voted for change. 100 days since Mirror readers put their trust in Labour. 100 days since we showed the Tories the door after 14 long years.
And 100 days since I stood on the steps of Downing Street and promised my government would always work for the people of this country.
That work of change began immediately.
In three months, we've done more than the Conservatives managed in the last 14 years.
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