So, who will be next? Let's look at some of the favourites...
Ian Austin (Lab, Dudley North). A Brownite and staunch enemy of Corbyn. He has been threatening to join TIG over the last two days, but people who make threats often can't be trusted. The Gang of Seven never made such threats. Furthermore, all of the current TIG members are staunch Remainers. Austin is not.
Guto Bebb (Con, Aberconwy). Resigned from the government to pursue a second referendum. A career politician he was a Plaid Cymru activist before joining the Tories, so would he sacrifice himself? Not yet perhaps, but if there is no Brexit deal...
Nick Boles (Con, Grantham & Stamford). A Remainer strongly tipped to be the next Tory to join TIG, but tweeted on Wednesday that he is "not ready to give up yet". Could be a late addition if there is no Brexit deal.
Neil Coyle (Lab, Bermondsey & Old Southwark). Nominated Corbyn for the leadership in 2015, but has since become one of his most brutal critics. Says he will stay, but clearly very unhappy when interviewed by the BBC. Could be pushed out eventually if the hard left push hard enough!
Stephen Doughty (Lab, Cardiff South & Penarth). It's been suggested that Welsh Labour defections are unlikely because Labour are in government there, but Welsh MPs sit in London. Doughty is a staunch Remainer and has been attacking the party this week on both Brexit and anti-Semitism. Has distanced himself from the quitters and is unlikely to quit any time soon.
Guto Bebb (Con, Aberconwy). Resigned from the government to pursue a second referendum. A career politician he was a Plaid Cymru activist before joining the Tories, so would he sacrifice himself? Not yet perhaps, but if there is no Brexit deal...
Nick Boles (Con, Grantham & Stamford). A Remainer strongly tipped to be the next Tory to join TIG, but tweeted on Wednesday that he is "not ready to give up yet". Could be a late addition if there is no Brexit deal.
Neil Coyle (Lab, Bermondsey & Old Southwark). Nominated Corbyn for the leadership in 2015, but has since become one of his most brutal critics. Says he will stay, but clearly very unhappy when interviewed by the BBC. Could be pushed out eventually if the hard left push hard enough!
Stephen Doughty (Lab, Cardiff South & Penarth). It's been suggested that Welsh Labour defections are unlikely because Labour are in government there, but Welsh MPs sit in London. Doughty is a staunch Remainer and has been attacking the party this week on both Brexit and anti-Semitism. Has distanced himself from the quitters and is unlikely to quit any time soon.
Angela Eagle (Lab, Wallasey). New Labour veteran and one of the longest serving MPs on the list. Most famous for challenging Corbyn for the leadership before backing out to allow Owen Smith a clear run. A Remainer and a member of Labour Friends of Israel, she's not said much this week and could spring a surprise, but would she take her twin sister with her...
Maria Eagle (Lab, Garston & Halewood). Twin sister of Angela and elected the same year, but infinitely more low profile and not much is known about her. Not a dickie bird about TIG this week.
Louise Ellman (Lab, Liverpool Riverside). Jewish MP and Remainer under attack from Momentum, she has pledged to stay and fight anti-Semitism from "within".
Justine Greening (Con, Putney). Another proponent of a second referendum, she has said nothing about any of the defections this week. Dark horse.
Louise Ellman (Lab, Liverpool Riverside). Jewish MP and Remainer under attack from Momentum, she has pledged to stay and fight anti-Semitism from "within".
Justine Greening (Con, Putney). Another proponent of a second referendum, she has said nothing about any of the defections this week. Dark horse.
Dominic Grieve (Con, Beaconsfield). Has been pretty blunt about his resignation prospects and says he will resign the whip if May takes us into a no deal Brexit. On that basis he won't be joining TIG for a few weeks.
Sam Gyimah (Con, East Surrey). Staunch Remainer who resigned as a minister in order to pursue a second referendum. Had been quiet this week, except to retweet Soubry's resignation, but later clarified that the retweet didn't mean he was going to "follow suit".
Peter Kyle (Lab, Hove). A staunch Remainer and Blairite, Kyle refused to sign the outlandish Corbyn loyalty pledge that did the rounds on Twitter earlier this week. However, on Wednesday he tweeted that he is "not about to quit".
Phillip Lee (Con, Bracknell). Caused a bit of a stir on the BBC on Wednesday by referring to Brexit as a "turd". Has been quoted as saying the "timing is not right", so could potentially quit in the event of a no deal Brexit. Tick tock, tick tock...
Phillip Lee (Con, Bracknell). Caused a bit of a stir on the BBC on Wednesday by referring to Brexit as a "turd". Has been quoted as saying the "timing is not right", so could potentially quit in the event of a no deal Brexit. Tick tock, tick tock...
Siobhain McDonough (Lab, Mitcham & Morden). Blairite Remainer, bit of a non-entity, but thought to be close to TIG's Chris Leslie. Probably too delicate to jump ship on her own.
Alison McGovern (Lab, Wirral South). Blairite Remainer who categorically denied in a live TV interview last week she would be quitting. She's gone a bit quiet this week, so could possibly reconsider if the hard left make things uncomfortable enough.
Ian Murray (Lab, Edinburgh South). Corbyn critic, Blairite and Remainer. Murray has publicly defended the Gang of Seven this week and has been on the receiving end of lots of hard left abuse in the process. One to watch.
Jess Phillips (Lab, Birmingham Yardley). Loudmouth Jess likes to be the centre of attention and has suggested she finds it hard "to disagree with a lot of what they [TIG] are saying". Not sure what her particular axe to grind is and she is not under threat from Momentum. Wild card.
Jess Phillips (Lab, Birmingham Yardley). Loudmouth Jess likes to be the centre of attention and has suggested she finds it hard "to disagree with a lot of what they [TIG] are saying". Not sure what her particular axe to grind is and she is not under threat from Momentum. Wild card.
Ruth Smeeth (Lab, Stoke-on-Trent North). A Corbyn critic, a Remainer, but not a big remoaner. As a Jewish MP receiving similar levels of abuse as Luciana Berger she was strongly expected to quit, but in an article for the Jewish News on Wednesday she said she is staying.
Owen Smith (Lab, Pontypridd). Failed leadership challenger Owen is one of the most unapologetic remoaners in Parliament and most tellingly has said nothing about TIG all week. Biding your time Owen?
Wes Streeting (Lab, Ilford North). Another Corbyn critic and staunch Remainer. Dismissed rumours of his departure by tweeting "I'm with her" in support of Ruth Smeeth's decision to stay.
Tom Watson (Lab, West Bromwich East). The left would dearly love to see the back of Watson, but it's not likely in the short term. As the elected deputy leader he can't be easily dislodged, but Corbyn and his followers have done everything they can to exclude him from proceedings. His response to the Gang of Seven was generally supportive of them and highly critical of Corbyn and Momentum. Watson is fearless and he won't quit.
Phil Wilson (Lab, Sedgefield). Staunch Remainer and critic of Corbyn. Very supportive of Tom Watson's damning response to the breakaway, but not a word on whether he would stay or go. Another one to watch.
Wes Streeting (Lab, Ilford North). Another Corbyn critic and staunch Remainer. Dismissed rumours of his departure by tweeting "I'm with her" in support of Ruth Smeeth's decision to stay.
Tom Watson (Lab, West Bromwich East). The left would dearly love to see the back of Watson, but it's not likely in the short term. As the elected deputy leader he can't be easily dislodged, but Corbyn and his followers have done everything they can to exclude him from proceedings. His response to the Gang of Seven was generally supportive of them and highly critical of Corbyn and Momentum. Watson is fearless and he won't quit.
Phil Wilson (Lab, Sedgefield). Staunch Remainer and critic of Corbyn. Very supportive of Tom Watson's damning response to the breakaway, but not a word on whether he would stay or go. Another one to watch.