The Shadow Foreign Secretary Douglas Alexander has said the Prime Minister is "out of touch at home and out of his depth abroad".
He is accusing David Cameron of isolating Britain in the European Union.
Douglas Alexander has started his speech by quoting the British distance runner and double gold-medalist Mo Farah.
When asked by a reporter whether he would have preferred to compete in the Olympics for his native Somalia, Mr Farah replied: "Listen mate, this my country. This is where I come from and when I put on a Great Britain vest I am proud. I am very proud."
The Shadow Foreign Secretary Douglas Alexander is taking to the stage at the Labour conference in Manchester. Watch a live video feed of his speech here.
Shadow foreign secretary Douglas Alexander has branded David Cameron's possibility of an EU referendum as a sign of 'weakness'.
"These latest statements about the possibility of an EU referendum reveal more about David Cameron's present weakness than his future plans.
"Ruling out a referendum one day and then ruling it back in again the next looks like a Prime Minister spending more time managing his party than leading the country.
"David Cameron seems to be more concerned with securing headlines about Europe than securing vital reforms within Europe."