Jewish voters have deserted Labour in the wake of the anti-Semitism row, John Mann MP has said.
Mr Mann, who confronted Ken Livingstone over comments he made about Hitler, said Labour should have been enjoying a "landslide" victory.
He told the BBC: "It is clear that the Jewish vote, which for generations in families has been Labour, has gone against Labour tonight. We have seen that in Bury, we have seen it in Glasgow, I think we will see it tomorrow in parts of London.
"This is a huge challenge, it's going to define Jeremy Corbyn's leadership. He has to lead from the front and get on top of this problem."
But the Labour MP insisted "now is not the time" for any challenge to Mr Corbyn.
More than 400 packs of new psychoactive substances have been seized by Nottinghamshire County Council in a raid of a Bassetlaw shop.
The substances are also known as ‘legal highs’ and are often branded and labelled in packaging which can fool both businesses and customers into believing they are safe to sell and consume.
The packs seized were labelled with brands such as ‘Charly Sheen’, ‘Go Gaine’ and ‘Bubblegum Bush’ and the council says it is carrying out tests to identify the chemicals that they contain.
A spokesperson said: "So called ‘legal highs’ contain a cocktail of chemicals which have often never been used in drugs for human consumption so have not been tested to check they are safe. Essentially, you are taking your life into your own hands by taking these substances."
John Mann the Bassetlaw Labour MP has criticised plans to have a two tier A&E service. He says it would down grade hospital care in rural areas
The golfer Lee Westwood was presented with a scroll and jewel of office at a special ceremony at Retford Town Hall. The 38-year-old from Worksop is the first person to become an Honorary Freeman of Bassetlaw in Nottinghamshire.