Separately for equities and long conventional gilts, I have charted 3 annualised returns over 10 years and 15 years. They are [a] UK in sterling (blue), [b] US in dollars (red) and [c] US converted to sterling (grey). It is simply not the case that US_£ will always be lower than UK_£ (the relative numbers are shown). Nor is the currency correction always beneficial (see “parity exchange rate”). The numbers in the main table, from top down, are mean, standard deviation, minimum and maximum.

While more detailed statistics are shown on the charts (see navigation buttons on left), the table shows that, on average, over 10 years and 15 years, the US equity return (converted to sterling) was higher than for the UK. However, that was the case for 21 (of 45) over 10 years and 22 (of 40) over 15 years.