The jokes are all over the internet. A dog is shown surrounded by a shredded cushion or cardboard box. Another is climbing up to eat stew from a pot on the kitchen stove. Whatever the situation, the punchline is the same: "I cannot comment until Sue Gray has completed her investigations."

Until a couple of weeks ago Sue Gray was "the most powerful person you've never heard of". Then, when she was put in charge of investigating parties at 10 Downing Street during lockdown she became a household name in the UK. Her report on "Partygate" is expected this week, and if it finds that the prime minister knew about the illegal gatherings, Johnson could be forced to resign.

Other top civil servants might welcome the limelight, but Gray has always kept a low profile. Even those who worked with her for years do not know where she grew up.

This secrecy has led some to believe that she is a spy. 

Gray's official title is Second Permanent Secretary to the Cabinet Office. But in an earlier role as Director-General, Propriety and Ethics, she was in charge of deciding whether ministers had broken rules. 

The role involved knowing everything about senior figures that might embarrass the government. It gave her a say in who was appointed in Cabinet reshuffles, and who was nominated for a knighthood or a seat in the House of Lords. 

As someone who can make or break a political career, her nicknames include "The Enforcer" and "The Grim Executioner". 

There is a softer side to her: because of her love of cats, the Cabinet Office now has two - Evie and Ozzie. She is also brilliant at karaoke. But no one doubts that her report will be ruthlessly professional, and make uncomfortable reading for Johnson. "I know Boris will represent everything she doesn't like," says one former minister. 

One of the few definite things known about her is that she did not go to university. She joined the civil service straight from school, starting at the most junior level.

Many other people have risen to the top without a university education. Alan Sugar and Richard Branson both left school at 16. Bill Gates, Mark Zuckerburg and Steve Jobs all dropped out of college.

Yes: For most people, education is the key to success. University does not just increase your knowledge, it provides a chance to expand your mind by mixing with clever people from many different backgrounds.

No: To be a success, you should start work and learn the ropes of the real world as soon as possible. Going to university will saddle you with an enormous student loan which will take years to pay off. 

Or... You will get more out of university if you go later in life rather than straight after school. You will have a better idea of what really interests you, and focus on your studies instead of partying.

Partygate - Nickname given to the controversy over a series of illegal gatherings hosted in 10 Downing Street, Johnson's office and home, during the Covid-19 lockdown.

Limelight - Public attention. The phrase comes from an early form of stage lighting which involved heating lime.

Cabinet Office - The Cabinet Office is part of the centre of government, alongside No 10 Downing Street and the Treasury. Its head office is near Downing Street. 

Propriety - Following correct behaviour.

Alan Sugar - His company Amstrad was among the first to sell affordable home computers. He is also known as the star of the TV series The Apprentice.

Richard Branson - His businesses have included Virgin Records, Virgin Trains and the space-tourism company Virgin Galactic.