Theresa May will call for opposition parties to "contribute" to the government's Brexit plans, in a major speech on Tuesday 11 July.

The prime minister's address will mark her one-year anniversary in Downing Street and will come more than a month after the general election, which left May weakened and wounded as the Conservatives lost their majority in the House of Commons.

The Tory premier has since gone on to secure a "confidence and supply" agreement from Northern Ireland's Democratic Unionist Party. But with just under five years of the current parliament left, May will reach out to Labour and face political reality.

"Though the result of last month's general election was not what I wanted, those defining beliefs remain, my commitment to change in Britain is undimmed; my belief in the potential of the British people and what we can achieve together as a nation remains steadfast; and the determination I have to get to grips with the challenges posed by a changing world never more sure," she will say.

"I am convinced that the path that I set out in that first speech outside Number 10 and upon which we have set ourselves as a government remains the right one. It will lead to the stronger, fairer Britain that we need. It will deliver the change people want.

"It will ensure we make the most of this opportunity to ask ourselves what kind of country we want to be and to answer that question with confidence, optimism and hope."

The speech, which is to be delivered at the launch at the Matthew Taylor report into the gig economy, marks a dramatic shift in May's election campaign tone. The prime minister then refused to back down over her so called "hard Brexit" demands, such as quitting the EU's customs union and single-market.

"When I commissioned this report I led a majority government in the House of Commons. The reality I now face as Prime Minister is rather different," May will say.

"In this new context, it will be even more important to make the case for our policies and our values, and to win the battle of ideas both in Parliament as well as in the country.

"So I say to the other parties in the House of Commons... come forward with your own views and ideas about how we can tackle these challenges as a country.

"We may not agree on everything, but through debate and discussion – the hallmarks of our Parliamentary democracy – ideas can be clarified and improved and a better way forward found."

But May's words are unlikely to stop her Great Repeal Bill, which is tabled before parliament on Thursday, facing a rough time in the House of Commons. The draft legislation is designed to immediately put all EU law into UK law on day-one of Brexit.

"The PM is promising to take big decisions in the long-term interests of Britain," said Tom Brake, the Liberal Democrats' Brexit spokesman.

"Her first such decision must be to negotiate to keep the UK in the Single Market and the Customs Union. This is in the long term interests of British prosperity, jobs and families.

"A bad deal or no deal at all, will do permanent damage to our economy which is already affected by Brexit blues."