04/05/2016 11:05 BST | Updated 05/05/2017 06:12 BST

Local Elections 2016 - This Week's Real Contests to Watch

Local elections are curious things. In many ways, they're a national conversation about the state of the parties in the middle of a Government's time in office. But on the other hand they are hundreds of individual by-elections, each with their own issues, casts of characters and unpredictable outcomes that can be maddeningly difficult to predict. While the media's attention is on the upcoming European Referendum, the entire country goes to the polls this week to decide on local councillors, the make-up of governments in the devolved administrations, who their local mayors will be and more. Regardless of the outcome of the referendum in June, this week will be a huge challenge for both David Cameron and Jeremy Corbyn and could help seal their fates as leaders.

So what would a good night be for either party? Traditionally, mid-term elections see the governing party in Westminster lose council seats across the country as voters take the opportunity to protest. Cameron would normally expect to be forgiven for taking a bit of a drubbing as a result. But this time around, the polls show that Corbyn's Labour are set to lose at least 100 councillors and possibly many more across England. That would be a remarkable result, even before you factor in Labour possibly having to go into coalition in Wales and, worse, being forced into third place behind the Conservatives in Scotland.

Expectations on the Prime Minister are now a lot higher than usual, and much lower for the Leader of the Opposition. Cameron will hope to repeat the success he had last May and pick up a number of wins in key council areas such as Harlow, Dudley and Southampton. In fact, Labour's poll ratings are so abysmal that, outside of London, it might be considered a failure if the Conservatives lost seats or just held steady.

Jeremy Corbyn, meanwhile, has set his own bar by vowing that Labour will not lose any councillors this May. Privately, many in the party are conceding that heavy losses are inevitable. Labour will hope to see wins in places like Bristol, where its popular mayoral candidate Marvin Rees is looking to unseat a maverick independent. Also keep an eye on Norwich, where Labour's real opposition has been the Green Party. Winning over "fellow travellers" from across the left has been a key selling point for the Corbyn wing of the party and this will be a test of how successful that strategy might be.

But the real complicating factor this May is UKIP. Nigel Farage's party could make significant gains this year, potentially winning list and regional seats in the Welsh Assembly and Scottish Parliament for the first time. UKIP's success will also be an important barometer for the other parties. Conservative losses to UKIP will worry David Cameron as he looks ahead to the referendum and considers its impact on his own authority as Leader. Further UKIP wins in Labour heartlands in the North and the Midlands will also be deeply concerning to a Labour party fearful of eroding its traditional core vote.

Apart from the London mayoral election, the headline act this week, many of these local contests will be seen as staging posts on the way to the EU vote next month. But rest assured that these results will be poured over by both party leaders as well as by their opponents. Each vote cast and each seat won will be marked on the balance sheet that will decide if, or when, either Cameron or Corbyn might be asked to step aside - for the good of their party, or for the good of the country.

At ICG, we have developed a guide to the 20 Contest to Watch on Local Election Night 2016. It lists the most interesting races in the elections to English Councils, the Welsh Assembly, the London Assembly and the race to become Police and Crime Commissioners. You can find our guide here.