Why better British fighters would not end Lend-Lease

Would Britain still use Lend-Lease carrier aircraft if its own 1939 designs were as good as American types?

Yes. Britain might start with a better fighter yet still need American production and a U.S.-built successor as wartime demands grew.

Even if Britain began the war with carrier fighters as capable as American designs, American aircraft would remain useful. Bombing placed pressure on British production. A better fighter at the outbreak of war would not guarantee that Britain could supply its successor on time. American production could still provide the next generation around 1942.