Welcome to another day at Westminster, where we'll be covering events in the Commons and Lords chambers. It's going to be a busy day, so thanks for joining us.

And that concludes our political coverage for this evening, we will be resuming on Thursday morning.

You can still follow the latest updates on the main news story.

Here are the main points:

• Defence Secretary Sir Michael Fallon has quit, citing his "previous conduct"
• Theresa May is widely expected to name a replacement tomorrow
• Sir Michael had earlier apologised for touching a journalist's leg at a dinner in 2002
• Sir Alan Duncan, Penny Mordaunt, Rory Stewart and Tobias Ellwood are among the contenders being named on social media

The World Tonight

The journalist who had her knee touched repeatedly by Sir Michael has come to his defence as a likeable minister who she is sad to see go.

Speaking to BBC Radio 4’s The World Tonight, Julia Hartley-Brewer said: “I like Sir Michael Fallon, I have always got on very well with him and… I have always had a good, friendly, bantery relationship [with him], which is why I didn’t take the issue seriously at the time and haven’t since.”

Responding to his resignation letter, where he said he had “fallen short” of the standards expected of the UK military, she said: “I doubt that we have such high expectations of every single person in the military that they have never touched a woman’s leg under the table.”

Ms Hartley-Brewer added: “If he has gone because he touched my knee 15 years ago, that is genuinely the most absurd reason for anyone to have lost their job in the history of the universe, so I hope it is not because of that.”

Laura Kuenssberg
BBC political editor

"What might have been acceptable 15, 10 years ago is clearly not acceptable now," Sir Michael Fallon told me tonight as he quit the government.

Clear to him now, and his departure will make clear to any other politicians in Westminster that behaviour they might have laughed off or treated as part and parcel of the rumbustious life is not acceptable and is not, it seems, acceptable to Number 10.

It has plainly for him been a very painful discovery to make.

Sources close to him don't believe that he is some kind of predator.

Read more from Laura.

The World Tonight

Former Conservative leader Iain Duncan Smith said he was sorry to see Sir Michael go, but it showed leadership from the prime minister who “read the riot act” to her cabinet.

He told BBC Radio 4’s The World Tonight: “Theresa May made it very, very clear… that it was simply unacceptable that people in positions of power over others should then abuse that position to solicit things that otherwise would not be granted to them.

“I understand she read the riot act to her cabinet in no uncertain terms and said she herself would not tolerate any kind of behaviour which either they have done previously or were engaged in.

“I think that has made it very clear to everybody, therefore if there is anything at all… then I am afraid you have no place in the cabinet and I think Michael Fallon took his decision on that basis.”

Tobias Ellwood is one of those being named as a potential contender for Defence Secretary.

Currently a junior minister in the Ministry of Defence, he served in the Royal Green Jackets from 1991 to 1996 with tours in Northern Ireland, Cyprus, Kuwait, Germany, Gibraltar and Bosnia.

He also tried in vain to save the life of PC Keith Palmer, the policeman killed in the Westminster terror attack in March - an experience Mr Ellwood says he still has "vivid memories" of.

• Tobias Ellwood: 5/2
• Boris Johnson: 6/1
• Penny Mordaunt: 6/1
• James Cleverly: 8/1
• Mark Lancaster 8/1
• Tom Tugendhat: 8/1
• Jacob Rees Mogg: 10/1
• Rory Stewart: 12/1
• Alan Duncan: 16/1
• Ben Wallace: 16/1

Sir Michael's resignation comes as MPs have been sharing their stories of inappropriate behaviour in Parliament.

Earlier this week, Labour MP Chi Onwurah says she complained about conduct in a Westminster bar - but said: "I was told that happens in pubs all over the country."

Read more claims made by MPs

Image source, PA

As soon as Sir Michael's resignation was announced, the chatter of a potential successor began in the corridors of Westminster.

Several newspapers and the BBC's Laura Kuenssberg have said MP for Portsmouth North Penny Mordaunt.

The current minister for disabled people has form in this area, as the only female Royal Naval reservist sitting in parliament.

The daughter of a paratrooper, she was named after the Leander-class frigate HMS Penelope.

She was also defence minister between 2015 and 2016.