In the UK the regulation is very strict, especially for foreign students. Need to submit by the end of 4th year and finish viva within five. years. If not, end up with complimentary MPhil or nothing.

Got a fellow candidate who submit against his supervisor's advice. Thesis end up below par, given another year to submit (first draft) but still not satisfactory. Five years wasted.

Heard quite a lot of story like that. My office mate was even stuck during proposal session at the end of the first year. The school changed their course offer to MPhil instead. So they quit rather than doing MPhil.

Another story I heard, a student failed their viva, twice. Luckily given a third chsnce and passed at the end.