Get the debate over Trident renewal wrong and it might be trade union leaders – rather than the PLP – that Jeremy Corbyn has to worry about most writes Keiran Pedley

Despite a difficult few days, Jeremy Corbyn seems to have emerged from last week’s reshuffle stronger than ever. He may not have got the Shadow Cabinet that he really wanted but piece by piece the Labour leader is shaping the party’s top team in his own image. The steady drip, drip, drip of resignations that followed last week’s reshuffle was unhelpful but as long as party members are behind him, it is hard to see any meaningful challenge to Jeremy Corbyn’s leadership for the time being.  For now, Labour moves on to yet another divisive battle – this time over the renewal of Trident.

On face value, the Labour leader might be confident of winning this battle too. He now has a Shadow Defence Secretary in Emily Thornberry that supports his policy of unilateral nuclear disarmament (so no Hilary Benn style speeches on this issue) whilst he should also be confident of the support of party members too.  A recent poll showed Labour voters opposing renewal by 40% to 31% with opposition among members likely to be greater still. Despite the official Labour Party policy being to support renewal, there are some in Labour that fear a change in policy is only a matter of time.

However, not only is a change in policy not inevitable but the upcoming debate over Trident may leave Jeremy Corbyn’s continued leadership of the Labour Party in doubt as well.

Two developments have taken place this week that we should pay close attention to. The first relates to a series of comments made by Sir Paul Kenny of the GMB. Speaking to Radio 4 on Monday, the union’s general secretary articulated the GMB’s continued support for the renewal of Trident in no uncertain terms:

“If anybody thinks that unions like the GMB are going to go quietly into the night while tens of thousands of our members’ jobs are literally swannied away by rhetoric then they’ve got another shock coming.”

The second development – along similar lines – relates to a piece in the Huffington Post today in which Paul Waugh outlines how Unite is likely to reconfirm its continued support for Trident this summer. Unite of course is Britain’s biggest union and Labour’s largest financial backer.

If both the GMB and Unite end up supporting the renewal of Trident then Jeremy Corbyn should be worried.  Sir Paul Kenny and Len McCluskey are no dictators but the Labour leader can ill afford to lose their support by falling out with them over this issue. An untold story of last summer’s Labour leadership contest is the financial and organisational muscle that the unions – especially Unite – provided the Corbyn campaign. If he loses their support then Corbyn could end up being very isolated indeed in the face of a disgruntled PLP and what promises to be a difficult set of elections in May (maybe London aside).

This all matters because a shift in attitudes towards Corbyn among trade union leaders could encourage his opponents in the PLP to move against him. On last week’s PB/Polling Matters podcast, Damian McBride outlined how party leaders are often removed through the sheer force of pressure on them to resign rather than because of an actual leadership contest.  If Labour does badly in May and MPs move against him then a statement by Kenny or McCluskey urging Corbyn to step aside would be fatal to his leadership. Rather than fight over Trident, the unions themselves may decide that it’s better to throw their weight behind someone like Owen Smith – or another left-winger – that comes without Corbyn’s 1980s baggage and ultimately has a better chance of winning a General Election.

So in the coming weeks Jeremy Corbyn is going to have to decide how much he is willing to risk over Trident. He is certainly going to have to tread very carefully. A fight with Unite and the GMB is not in his interests right now and you can bet that his opponents in the PLP are watching developments very closely. Corbyn’s position as leader of the Labour Party might seem strong right now but if he loses union support over Trident then that could change very quickly.

Keiran Pedley

Keiran Pedley is an elections and polling expert at GfK and presenter of the PB/Polling Matters podcast.  Please support the podcast by ‘liking’ our Facebook page here. Keiran tweets about politics and public opinion at @keiranpedley.