Further profit warnings expected

'Sell in May and go away' is one of the oldest mantras in the fund managers' training manual. Investors who heeded this advice in 2001 will, by now, be feeling fairly pleased with themselves. At the time of writing, the broad index of UK shares was nearly 10% below May's high. US share prices have also headed south. What has caused markets to fall? A constant flow of high profile companies warning that profits will be well below analysts' expectations hasn't helped. The fact that some of these expectations were unrealistically high to start with doesn't matter. The painful truth is that i...