People think that investment is complicated, and sometimes it is. But sometimes is it just too easy?

Take British Land, the commercial property company. The business is hardly difficult to understand. It owns a bunch of office properties in the City of London, including the enormous Plantation House, some shops in out-of-town centres and a few other bits and bobs. If the market value of the company is higher than the aggregate value of the properties, the shares will seem expensive. If the share price and the net asset value (NAV) per share are about the same, it can be assumed that the shares are fairly valued. And if, like now, shares trade well below NAV, shares are cheap.

A quick glance at the chart shows that British Land shares are often mispriced relative to the underlying value of the properties it owns. In 2003 shares were priced at less than half the value suggested by the NAV. Early last year the shares changed hands for considerably more.

Happily, it also seems that the share price follows changes in NAV, leaving open the chance to draw financial benefit from the disparity. The best returns will come to the nimble movers, but if history repeats itself, shares in British Land will rise to meet the NAV and may subsequently move beyond. Those that buy shares at 825p can reasonably expect to make a 50 per cent return over the next couple of years.

There are, of course, caveats. Even when investment looks easy, you have to consider eventualities that might add layers of complexity. The first doubt is that history will not repeat itself and/or lead us to inaccurate conclusions. But history has repeated itself before, and if we begin to distrust the lessons of the past, we remove one of the few sets of reference points available. Secondly, asset valuation calculations may be misleading. If they were unerringly accurate, the share price would surely stay in closer alignment. NAVs may not reflect the underlying value of the company, thanks to swift movement in the real cost of debt and tax liabilities. The real value of property moves according to the health of the economy and shifting patterns of landlord supply and tenant demand.

The biggest worry, however, is that the latest NAV figure will be followed by others that are lower. Future NAVs may be nearer, or below, the current share price. If they are, hindsight may well show that the shares, at present, are far from being the bargain they appear.

Stephen Hester, the British Land chief executive, was hardly upbeat when presenting annual results last week. “We remain in a stressed economic and market environment,” he said. Commercial property values may continue to fall if the economic climate continues to cool. Retailers and big City companies are important customers for British Land, and neither are enjoying the kind of confidence that feeds the temptation to relocate or open new branches.

As demand wilts, newly developed properties come on to the market and add to problems caused by softening demand. If rents drift lower, values do too. Meanwhile, the credit crunch may change the true cost of debt carried by companies.

British Land, however, seems to enjoy protection against most of the obvious threats. As much as 99 per cent of its properties are occupied and the average unexpired lease is nearly 15 years. Meanwhile, 100 per cent of its debt is fixed, for a period of nearly 13 years at an average rate of 5.29 per cent. Most telling of all, the average rental yield on its properties is 5.6 per cent.

You would expect commercial property to provide more income than equities because there is less likelihood that the income will rise, and more than bonds because physical properties are more cumbersome to manage. But the rental yield suggests that British Land properties are soundly valued, with ten-year gilts giving 4.8 per cent and London-listed equities yielding less than 4 per cent. They may even be a little on the cheap side. That only makes the shares - trading at a 40 per cent discount to stated NAV - look all the more attractive. Buy.

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