And did again, in pretty similar circumstances in The Eleventh Hour!!
The Eleventh Hour was the third time it happened, the newly regenerated eighth Doctor also took his clothes from a hospital.
I was more surprised at the fact that it would happen on TV in 1970 than by the Doctor doing so. I would've thought that TV, especially children's TV, in that era had stricter rules about heroes doing illegal things.
He steals a car as well, but there's a scene right at the end of Spearhead...
that acknowledges both, when the Brig insists that the car must be returned to its rightful owner, although the Doctor asks to be given something similar (leading to Bessie's introduction in the next story). He then realises that he doesn't even own the clothes he's wearing - "I borrowed them from the hospital!" - which implies that he returns them too, and then takes to wearing an identical outfit of his own.
By the time of the TVM and The Eleventh Hour
however, he seems to have become a bit more carefree about such things (cases of the writers homaging Spearhead...
without the original's acknowledgement of the theft, although he did "borrow" the TARDIS after all so there's a precedent):
"You kept the clothes?"
"Well, I just saved the world, the whole planet, for about the millionth time, no charge; yeah, shoot me, I kept the clothes!"