Fund managers are taking larger stakes in FTSE 100 stocks, putting the companies at greater risk of a sudden change in control.

One in five of the 100 leading UK stocks have shareholders with holdings of more than 10%. The top three owners by percentage holdings are Capital Group, which owns 17% of medical supplies company Smith & Nephew, Amvescap, which holds 15% of power station group Drax, and Franklin Templeton, which has 15% of caterer Compass Group, according to data compiled by Financial News. Last week's dawn raid on the London Stock Exchange by US rival Nasdaq, which bought Scottish Widows Investment Partnership's 3.3% stake, coupled with Fidelity's sale the previous week of its 11.4% stake in ITV to BSkyB, has highlighted the vulnerability of UK companies to sudden sales by shareholders. In April, Threadneedle Investments sold its 14% stake in the London Stock Exchange to Nasdaq. The Takeover Panel this year abolished rules to prevent investors buying more than 14.9% of a company in a single transaction. That has opened the door to sudden raids by companies for big stakes. Companies have mixed views about the rule change. "There is the risk it makes the job of a corporate buyer that wants to accumulate a stake quickly that bit easier," said the head of investor relations at a FTSE 100 company. Investor relations managers confirm stakes in the largest companies have become bigger. Miriam McKay, head of investor relations at news group Reuters, said: "When you get concentration like that there are positives and negatives. On the one hand, if you've got a supportive shareholder doing in-depth research and building a big position that can be a strong endorsement. "But the flip side is that big position can form a block that is more easily swapped out. In our experience the depth of the research we have seen behind our largest shareholder is impressive and they have been very supportive." Fidelity has a 14.9% stake in Reuters. Andrew Jones, head of investor relations at Drax, said: "It means we have a good understanding of what our shareholder base wants." Amvescap and Threadneedle each hold more than 10% of Drax. Andrew Kirton, head of investment consulting at Mercer in Europe, said concentration of stock positions was an issue his company looks at when researching fund managers. "When markets started falling in the early part of the decade, some value managers owned more than 20% of some medium-sized stocks and, although those stocks performed well over the next few years, because they were losing business they became a forced seller in falling markets. It was savage at the time," he said. Martin Cobb, a UK equity portfolio manager at Franklin Templeton, which has a 15% stake in Compass, said: "We do a lot of negotiating with management behind closed doors, so we're not what you'd call a classic activist. We have no ability to run companies and we are typically supportive of management. Something like ITV/BSkyB sounds exceptional, but may become more the norm." Investment consultants said part of the reason for managers taking larger positions in FTSE 100 constituents was that they find better value in large caps than in small and mid-cap names.