The Monica Lewinsky affair is not the point. That's not what you're voting for. It's whether you can keep the country running. In the United Kingdom there are no primary elections along US lines, nor would such a system be easy, because the timing of general elections is unpredictable. The House of Commons is elected for a maximum term of five years.
Voters usually get three weeks' notice of a general election.
The expenses of parliamentary candidates are strictly limited. These provisions and uncertainty about the timing of an election produce inexpensive campaigns which are very short by American standards. Uncertainty about the timing of a general election, has produced the British phenomenon of the Opposition. Its decisive characteristic is that it attempts to form an alternative government, ready to take office at any time. The leader of the Opposition is paid an official salary.