"Someone's just told me the English are still trying to take over the United States - is that true?"

The quote by Steve Guttenberg is likely describing the long-standing competition in between the United States and the United Kingdom. The 2 countries have actually had a tumultuous relationship considering that the American Revolution, when the United States stated self-reliance from the British Empire. Regardless of the 2 countries now being allies, there is still a sense of competition between them. The quote is likely a joke, as the United States is an independent country and the English are not actively attempting to take it over. It is a humorous way of acknowledging the enduring rivalry between the 2 countries.