Another World: A Wizard named Catweazle

This Grubby Disheveled Wizard named Catweazle, fleeing the sword blades of Norman Soldiers, packs up his Toad Familiar Touchwood and casting a Spell leaps into a pond only to emerge nine hundred years later...

He doesnt realy cast a gate, rather it is more like a wish (to be wisked away to safety), so as this is a nineth level spell, Catweazle is at least an 18th level Magicuser. His age is to be considered decrepid (over fifty). His brown robes are foul and stained and he reeks of a nasty odour. He has taken Toad as his familiar and until his departure to the future, he lives with his spellbooks and laboratory in a candle-lit cave.

Its probably one of the early UK Isekai to be had in children's TV viewing.