Vote of no confidence: what is the 1922 Committee and how many votes are needed for a leadership election?

A number of Tory MPs have submitted letters of no confidence in Boris Johnson, seeking to trigger a Conservative leadership election.

This comes after Johnson was forced to make a public apology at Prime Minister's questions yesterday after an email leaked to ITV showed that an outdoor party or 'gathering', involving an invitation to up to 100 people to 'bring your own booze', was held at Downing Street during lockdown in 2020.