Whisk the flour, sugar, baking powder, baking soda and salt together in a large bowl.
Whisk eggs and 1/4 cup oil in 2nd medium bowl until well combined.
Whisk milk and vanilla into egg mixture.
Add egg mixture to flour mixture and stir gently until just combined (batter should remain lumpy with few streaks of flour). Let batter sit for 10 minutes before cooking.
Heat 1/2 tsp oil in a nonstick skillet or frying pan over medium-low heat until shimmering. Using paper towels, carefully wipe out oil, leaving thin film on bottom and sides. Drop 1 Tbsp of batter in centre of pan. If pancake is pale golden brown after 1 minute, pan is ready. If it is too light or dark, adjust heat accordingly.
Using 1/4 cup, portion batter into pan in 3 places, leaving space between portions.
Cook until edges are set, first sides are golden brown, and bubbles on surface are just beginning to break, 2 to 3 minutes.
Using a thin, wide spatula, flip crumpets and continue to cook until other side is golden brown, 1 to 2 minutes longer.
Repeat with remaining batter, using remaining oil to coat pan as necessary.