Prime Minister Theresa May has said the government’s thinking on Brexit “isn’t muddled at all”.
Her comments on Sky News come after the UK’s former ambassador to the EU, Sir Ivan Rogers, criticised ministers’ approach to negotiations.
Mrs May said the government’s priority was to get the “best possible deal” and that she would set out more detail on her aims “in the coming weeks”.
Brexit talks with the EU are expected to begin as early as April.
Mrs May said it was not possible for the UK to hold on to “bits” of membership after leaving the EU.
There has been much debate in recent weeks about the nature of Brexit, and whether controls on the movement of EU citizens will mean the UK leaves and customs union.
The government has also come under pressure to reveal more of its plan.
Sir Ivan stepped down from his ambassador role on Tuesday, criticising “muddled thinking” among ministers. He has been replaced by Sir Tim Barrow.
Mrs May told Sky News’s Sophy Ridge on Sunday: “Anybody who looks at this question of free movement and trade as a sort of zero-sum game is approaching it in the wrong way.
“I’m ambitious for what we can get for the UK in terms of our relationship with the European Union because I also think that’s going to be good for the European Union.
“Our thinking on this isn’t muddled at all.”
But it was “important to take some time” to look at the “complexity of the issues”, she added.
Mr May said: “Often people talk in terms as if somehow we are leaving the EU but we still want to kind of keep bits of membership of the EU.
“We are leaving. We are coming out. We are not going to be a member of the EU any longer.
“So the question is what is the right relationship for the UK to have with the European Union when we are outside.
“We will be able to have control of our borders, control of our laws.”
In the referendum last summer, voters opted by 51.9% to 48.1% in favour of Brexit.
Mrs May said: “This is what people were voting for on 23 June.
“But of course we still want the best possible deal for us, companies to be able to trade, UK companies to be able to trade in and operate within the European Union and also European companies to be able to trade with the UK and operate within the UK.”
The prime minister has promised to invoke Article 50 of the Lisbon Treaty – getting formal Brexit negotiations with the EU under way – by the end of March.
Mrs May told Sky: “Over the coming weeks, I’ll be setting out more details of my plan for Britain. Yes, that’s about getting the right deal for Brexit, but it is also about economic reform…
“It’s about getting the right deal internationally, but it’s also about a fair deal at home.”
Earlier, Europhile former Conservative chancellor Ken Clarke told BBC One’s Andrew Marr Show: “Theresa needs to address the more serious question of the muddle [Sir Ivan is] complaining about, see whether she agrees with him and decide whether she can improve the way in which she organises the government to get to a proper conclusion.”
Liberal Democrat leader Tim Farron said Mrs May’s comments “confirmed she is taking us towards a disastrous hard Brexit that will leave our country poorer and more divided”.
But Richard Tice, co-chairman of the Leave Means Leave campaign, said: “We welcome the prime minister’s commitment to taking back control of Britain’s borders, therefore ending preferential treatment for EU citizens.
“She is right that issues of trade and immigration are not binary because when Britain leaves the single market and the customs union, though freedom of movement will cease, Britain’s ability to trade with the EU and access the single market will continue.”