The Thursday election win by Boris Johnson may be necessary to recover billions of pounds of investment.

An unexpectedly high parliamentary majority of 80 seats could make a major difference to UK equity–the laggard of the developed global stock markets over the last decade–with the resounding win for British Prime Minister Johnson, who campaigned largely against a Brexit deal slogan in January.

Not only does it bring clarity for the Brexit haze by the scale of the vote, but money managers say that it might make room for Joh....