The direct measures aimed at construction-related activities and businesses in the 2009 Budget will be welcomed in some quarters, mainly among the house builders.

Though I am not so sure I would go with the instant view from the surveyors’ body RICS that: “Measures announced by the Chancellor will help move towards a sustainable and vibrant housing market for the future.”

But time will tell.

From what I can see the various measures are small beer for the construction industry as a whole. Rather like taking one aspirin for a severe migraine.

If you added all the money promised for construction-related activity together and assumed some extravagant leverage on the injected cash you’d hardly fill the bottom of the huge hole appearing in the industry’s workload – a hole between £10 billon and £20 billion depending on which view you take.

Still it’s something.

For me though the worrying thing about this Budget is its optimism. Because if the growth forecasts prove wrong it is highly likely that construction will take more than a fair share of the pain when the public finances fall short of the Chancellor’s expectation.

Alistair Darling sees a fall in overall economic growth (on the GDP measure) down 3.5% this year. That is fair enough and in line with the consensus of forecasts.

But by the end of this year, he says, we will see growth emerging, which will propel us into an expansion phase with a 1.25% increase in GDP in 2010 and 3.5% in 2011.

That rate he says will be maintained until it shifts back to a “trend growth” of 2.75%.

Let’s have a look at what everyone else says.

Yes the consensus is for 3.5% growth this year. But if we look at the latest Item Club forecast we see 2010 at -0.1%, 2011 at 1.8% and 2012 at 2.5%. What’s interesting is that the Item Club uses the same economic model as the Chancellor.

And if you look at the consensus forecast produced by the Treasury itself you see the average view is for growth next year of about 0.3%, with just four of the 37 forecasts listed either as bullish or more bullish than the Treasury.

Given the spectacular over-optimism of the previous forecast six months ago, it is easy to speculate that it is in the Chancellor’s interest to lean to the upside on his projections.

Certainly the mesmerising growth in the national debt projected from here on would no doubt have been even more surreal had he chosen to balance his budget using different growth assumptions.

Given what appears to be reckless disregard for the downside risks. I am left wondering why he just didn’t go for broke and pump shed loads more cash into the construction industry – he would have got my vote had he done so.

So when you are doing your business planning I suggest that you bear in mind that, if his figures explode and he comes wild-eyed with a knife to public spending, construction absorbs a good £40 billion of taxpayers’ cash a year.

Will his figures explode?

Well I suspect that as the dust settles most economists will probably agree that they will.

As I have said many times, I am all for optimism, but when it edges towards delusion I start to worry.

But in this crazy world who knows, perhaps he will be proved right…I certainly hope so.