The monthly survey of 12 investment managers based in Britain found that the average exposure to equities in global balanced portfolios remained at the high reached in March, 54.3 percent.

Allocations to bonds were eased slightly to 23.4 percent from 24.2 percent. Investors also cut safe-haven cash holdings to 7.1 percent from 7.5 percent.

The biggest change in portfolios was an increase of more than 1 percentage point in exposure to alternative assets, including hedge funds and private equity, which averaged 11 percent in April.

Contributors to the poll attributed much of their bullishness on stocks to the fact that key central banks in Europe, Japan and China, are moving to stimulate moribund economies.

That has led many to favour assets away from the United States and Britain, where policymakers are moving in the opposite direction, winding down monetary stimulus put in place after the 2008-9 financial crisis.

"You must think slowly before you act fast, bend with the wind, which really leads you to those countries and central banks that remain accommodative... the European Central Bank and the Bank of Japan," said Peter Lowman, chief investment officer at Investment Quorum.

Standard Life Investments said it had re-aligned portfolios to favour Europe and Japan over the Untied States and Britain.

"The major change to the house view this spring has been a rotation away from the U.S. and UK equity markets, which are now Neutral in our portfolios, and towards the European and Japanese equity markets," Standard Life said.

However, the headline poll results obscure growing unease among investors that the tide may turn against stocks, following a period which has seen key markets reach record highs.

In particular, investors cited as risks to stability a possible exit of Greece from the Euro zone, an economic slowdown in China and the possibility that the United States Federal Reserve might mis-time planned interest rate hikes .

"The biggest risk to portfolios is a rise in U.S. interest rates concurrent with a stalling in U.S. economic momentum, given that Europe is still fragile and China appears to be slowing down," said Rob Pemberton, investment director at wealth management firm HFM Columbus.

(Reporting by Chris Vellacott; Editing by Larry King)

By Chris Vellacott