In a report on BBC On-line today, chief executive Carlos Ghosn says Nissan will pour more money into the Sunderland plant to start building its new Almera only if the UK has signalled it will join the euro.
Mr Ghosn warned if not, the company would take its money elsewhere.
Nissan wants to start building the replacement Almera in 2004.
Mr Ghosn said: "If the signs are clear and reassuring, we will reinvest in Sunderland. If there are too many risks we will go elsewhere. We want our main cost base in Europe to be in the same currency as our receipts."
The Sunderland plant, which builds the Micra, currently employs about 4900 workers