The next Ice Age could take only weeks to engulf Britain. Scientists say the last great disruption to the Gulf Stream 12,800 years ago took only a couple of months to trigger a massive plunge in temperatures across Europe.

"It was as if Europe had been shifted 20 degrees north and Ireland moved to Svalbard," said Bill Patterson of Saskatchewan University.

In the Hollywood blockbuster The Day After Tomorrow, an Ice Age was set off in a single day when the Gulf Stream was disrupted. "That is silly," said Patterson. "It couldn't happen that quickly. However, previous estimates that it would take decades to switch off the Gulf Stream are not backed by our work. It could happen in a couple of months."

The Gulf Stream carries tropical heat from the Caribbean to northern Europe but is already being disrupted by meltwater pouring from the Arctic as global warming intensifies. One day it may switch off completely, say scientists.

Such an event occurred 12,800 years ago when a vast lake – created from melting glaciers at the end of last Ice Age – overflowed and poured into the north Atlantic, blocking the Gulf Stream. Europe froze – almost instantly, said Patterson.

His team analysed mud samples from Lough Monreagh in Ireland and discovered layers of white sediment made up of calcite crystals from algae. "Then abruptly the sediment turned black. This stuff contained no biological material." In other words, all life in the lake had been extinguished in less than three months. "It was very sudden," added Patterson, "and it could happen again."