Long-term readers of Asset Allocator will remember that last year Justin Onuekwusi - then head of retail investments at Legal & General Investment Management - appeared on our podcast to express his concerns about concentration.

In particular Onuekwusi, who at the time led the team which ran LGIM's model portfolio, expressed concern about the growing influence of a handful of stocks within US equity indices and the growing influence of US equity indices themselves within global markets.

This week we happened to bump into Onuekwusi, who is now chief investment officer at St James's Place, and he said his concerns about concentration had not diminished.

In particular he highlighted the fact that in the US, the top 10 stocks have gone from 10 per cent of the index to more than a third of the index.

When we asked him how he sees this issue coming to a head or unwinding itself, Onuekwusi said: "We have seen some warning signs already with Google missing their earnings a few quarters ago and the impact that had on all of those stocks.

"What I worry about is you will have an earnings miss and people in those stock will pull liquidity out of the market.

"The managers we invest in don't necessarily have significant amounts exposed to those tech stocks but I am worried about liquidity, and the impact of rate movements on those large stocks. Small changes in rates mean those rates go up, those stocks go down."

Onuekwusi is underweight the US for this reason, among others, and he is overweight most other regions. He also thinks small caps are starting to look attractive - particularly in the UK. Indeed he thinks the UK in general looks very attractively valued at the moment.