Not me- but my boyfriend went into a flat-share when he did his summer internship over 6 years ago. He waited until last minute and took over a room in a share for the summer as the occupant was travelling over the summer months. You can always find accommodation in London.
Depending on whether or not your willing to share will be the ultimate decider in cost. You are better going into halls if you want a bit more privacy- but flatshares are cheaper over all.
We have said when we buy our house next year we won't get a lodger- but will consider letting out to students doing summer internships as to make a bit of money over the summer.