Hargreaves comments were made in a communication with clients of the Blue Whale Growth fund - a vehicle in which Hargreaves has a personal investment of more than £100mn.
He is also chair of Blue Whale Capital, the asset management firm that operates the fund.
Hargreaves retains a stake worth around £1bn in Hargreaves Lansdown, the FTSE 100 financial services firm, and so has a substantial exposure to the UK equity market and economy in that way.
In the correspondence, Hargreaves said that most UK-based investors are still underweight in America.
He said: “Currently there is much uncertainty and it seems sensible to seek the large successful companies in the safest economy.
"Blue Whale, for the time being will concentrate on investing in the USA and North America more generally.”
Hargreaves comments also included criticism of UK government policies.
He said: “Spend and borrow has prevailed no matter the alignment of governments red, blue and coalition alike. A trade gap has been a constant feature which has now reached unprecedented levels. If we include off balance sheet items, unfunded public sector pensions, PPI, student loans etc, then government debt is close to £4trn.
"This number is hard to comprehend, but I tend to use the following to explain - a million seconds takes 11 days to expire. One trillion seconds would take thirty two thousand years. Young voters will be the ones to inherit this debt, but there are no signs any would vote for a government willing to combat it."
Hargreaves added that the UK has had a fiscal deficit for over 20 year and so the total debt is growing.
"Currency movements in the short term are impossible to forecast, they are caused by sentiment rather than fundamentals," he said.
"Sterling has rallied since the Truss crash but in the medium term I am not optimistic in light of the above. Trade deals, of which we were optimistic, have faltered and the world is becoming more protectionist. We expect sterling to come under pressure.”
His comments on the UK political outlook should be seen in the context of Hargreaves being a substantial donor to the Conservative party and to the Brexit campaign in recent years.
He added that Europe has many of the same issues as the UK in terms of debt, energy supply issues and demographics, but he feels the US is immune from many of these.
Hargreaves said: “The USA was slow to combat inflation and still might need to impose further rate rises.