Complex sentence: The United Kingdom is by far the company's most successful export market in terms of cumulative sales volume, and at one point Proton set the record for "Fastest Selling Make of New Car Ever to Enter the United Kingdom".
Split into simpler sentences: The United Kingdom is by far Proton's most successful export market in terms of cumulative sales volume. Proton also set the record for the "Fastest Selling Make of New Car Ever to Enter the United Kingdom".