In a speech in London she will set out 12 key priorities for the EU negotiations, including an ambition to build new trading relationships with the continent.
Her plan is unlikely to see Britain adopting existing models such as deals between Norway, Canada and other countries with the EU.
She will say: “We seek a new and equal partnership – between an independent, self-governing, global Britain and our friends and allies in the EU.
“Not partial membership of the European Union, associate membership of the European Union or anything that leaves us half-in, half-out.
“We do not seek to adopt a model already enjoyed by other countries. We do not seek to hold on to bits of membership as we leave. The United Kingdom is leaving the European Union. My job is to get the right deal for Britain as we do.”
Sterling, which has already fallen on the speculation of a hard Brexit, is expected to come under further pressure.
It fell as low as $1.1988 on Monday, one of its lowest levels for 30 years, but has recovered slightly to trade at $1.2119 on Tuesday morning.
Wall Street was closed on Monday for Martin Luther King Day. Japan’s Nikkei .N225 brushed a five-week low and was last down 1.5%.
Mrs May’s priorities include control over immigration, regaining control of Britain’s borders, preserving the union, and removing Britain from the jurisdiction of the European court of justice.
She will also commit to retaining worker’s rights and making Britain an attractive place for investors and students through attractive taxes and tariffs.
Mrs May is being driven by four underlying principles: “certainty and clarity; a stronger Britain; a fairer Britain; and a truly global Britain”.
SNP hopes rejected
The SNP is likely to be left empty-handed, with no aspecial settlement for Scotland which wants a soft Brexit and is keen to maintain a flow of immigrant labour.
Angus Robertson, the party’s leader in Westminster, said: “We are deadly serious about protecting Scotland’s place in Europe and I would expect to hear that she is taking this seriously if making keynote speech about Brexit. But I’m not holding my breath.”
Mrs May was boosted before the speech when the International Monetary Fund – which had previously been negative on the impact of Brexit – upgraded its outlook for the British economy this year.
The IMF said it expected the UK to grow by 1.5%, up from a previous forecast of 1.1%.
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