Why are Labour MPs quitting the party? After many months of speculation, seven of them gave their reasons. At a press conference launching their new Independent Group of parliamentarians, they cited the Labour leadership's response to anti-semitism within the party; Brexit policy; and Corbynism itself as what drove them out.

Luciana Berger, the MP for Liverpool Wavertree, could not have been clearer as to her reasons for leaving. She has campaigned resolutely for a more robust response to anti-semitism within the Labour Party. She has been very open about what she has wanted the Labour leadership to do over many months – for instance, with the row last summer over the party's reluctance to adopt, in full, an international definition of anti-semitism (something it eventually did do in September). When she described bullying and bigotry in her speech, Berger was speaking from her experience within the Labour Party, and the abuse she has received on and offline. Berger's speech was powerful, and will be returned to many times over the coming months.

Brexit was mentioned a great deal on the platform. Labour's approach, certainly since the Brexit debates in British politics have become clearer, has been to seek to avoid blame, whatever the outcome. It has sought to avoid being blamed for the frustrations felt by those who voted Leave but has also tried to avoid being blamed for Brexit by any Remainers who might suspect the party of facilitating departure from the European Union rather than blocking it.

Some in the party were supportive of this studied ambiguity during the 2017 general election. Labour could not be pinned down on its Brexit position so attracted votes from both Leave and Remain camps. But now, as parliament hurtles towards a point where it must make a decision, this strategy has led to real fracturing.

Keir Starmer, the shadow Brexit secretary, has indicated that he knows the strategy has reached its end, but Jeremy Corbyn has so far sought to hold Labour's line. There is, no doubt, an incredibly difficult electoral coalition for any Labour leader to manage on this point. But having run for the leadership on the basis of resetting relations between members and MPs – including respecting the policy wishes of members – Corbyn's stance appears inglorious to some Remainers. The membership has, after all, shown significant support for holding a second referendum.

A new direction

Corbynism itself was highlighted by some of the MPs who have quit Labour and, of course, people have different views about what exactly Corbynism is. Chris Leslie, Angela Smith, Gavin Shuker and Mike Gapes all, to different extents and with different focuses, took issue with the Corbynite worldview. Anne Coffey brought this together in her contribution, using the language of Labour's "broad church". The old adage associated with Harold Wilson has been passed down through generations of Labour Party people. At its simplest, it is about doctrinal diversity and collegiality: that there are many definitions of Labour's socialism, and within the boundaries of democratic socialism all are welcome within the Labour Party.

The broad church mentality is key to preventing division from turning into rancour, but has too often been absent within the contemporary Labour Party. There should undoubtedly be great commonality within a "broad church" – even if such commonality is wilfully overlooked for factional reasons – but there need not be obedience.

Indeed, such a stance should be intrinsic to socialism. Policies can be criticised. Political strategies the same. As rumours swirled that the seven were about to announce that they'd quit the party, other Labour members – including some of the shadow cabinet – began making "loyalty pledges" online. The irony of people supporting a leader who draws strength from his past dissent, yet seeking to prevent any in today's Labour Party was not lost.

Chuka Umunna's contribution was the speech most focused on "what next?" Having been expected to run for the Labour leadership in 2017 had Corbyn lost the general election badly, his narrative was of a broken party system, and an appeal for others to leave their own parties and to support the Independent Group. These are the remarks that will, no doubt, see much speculation and discussion about a new party, and the lessons of the Social Democratic Party (SDP).

In terms of the effect of any new party on Labour, many of those who disagree with the decision to leave Labour will suggest the SDP experience points to years of Conservative rule. Ivor Crewe and Anthony King's book on the SDP – which must surely be reprinted – disagreed, and concluded that the "existence of the SDP did not materially affect the outcome" of the elections in 1983 and 1987. By the time of Kinnock's more comprehensive internal reforms post Labour's 1987 defeat, the SDP had ceased to be a threat.

The publication of a two-page statement of values by the Independent Group will also result in some comparisons with the SDP. It is useful to reflect on Shirley Williams' critique of a "centre party" – before she became one of the founders of the SDP – and what came to be seen as tests for a new grouping. A centre party, Williams had said, would have "no roots, no principles, no philosophy and no values" – a phrase, Crewe and King noted, she came back to repeatedly.

It is, perhaps, the roots and philosophy that any new group will find most challenging. Like-minded Labour MPs are likely to be able to coalesce around shared principles and values, but what of an alternative political philosophy? On this, the two-page statement from the group is very weak. And on battling the established parties, what deals will a new group make with the Liberal Democrats? Do you target one of the two major parties or both? We now know more about why these MPs left Labour, but little about where they go from here, or what unites their thinking.

Karl Pike, PhD candidate and Teaching Associate, School of Politics and International Relations, Queen Mary University of London This article is republished from The Conversation under a Creative Commons license. Read the original article.