Shares have gone through the roof: could they possibly go even higher?

As 2018 gets under way, there are clear signs that stocks are overvalued, but other factors are in play too. We ask two respected fund managers: what’s next?Shares are expensive – keep buying them. That appears to be investors’ consensus view. The storming run for stock markets in 2017 seemed almost too good to be trusted, but 2018 has started in similar style.In the US, the Dow Jones industrial average soared past 25,000 last week, almost exactly 12 months after 20,000 was ach