The sensitivities provided in budget 2009 are on pages 232 and 233. To take a rough approximation, if they were equivalent reductions in the volume and on the price side, as a simple average you'd probably end up with something around $2 billion in the first year for a 1% decline in nominal GDP. But the composition of that reduction matters crucially. If the reduction stemmed entirely from a reduction in real GDP, the impact would be probably around $3 billion or $3.5 billion. It's crucial to know what's driving the reduction in nominal GDP.
