Yes, but only in excellent conditions. From the Cliffs of Dover, with a height of about 100 m, your horizon would be at 35.7 km. You can calculate this distance with this formula, where h is your elevation and r Earth's radius:
a = √[(r + h)² - r²]
Since the narrowest part of the Channel is barely 33 km, you can see France, but by a hair's breadth. Read more