Union leaders have warned that cutting public spending would provoke a "double dip" recession, raise unemployment to over four million and spark the threat of mass industrial action. One senior official also reminded politicians that the last time the UK suffered "slash and burn" economics, there were riots on the streets. Ahead of the TUC Congress, starting tomorrow, the general secretary Brendan Barber said that the return of mass unemployment would have "terrible" social effects and could lead to Britain being "broken". As public spending emerges as a key issue ahead of next year's General Election, unions have spelled out their concerns on jobs and warned of industrial and social unrest. Mark Serwotka, general secretary of the Public and Commercial Services union, said he feared there will be "huge" spending cuts, whichever party wins the election. "Cuts will be quicker and deeper under the Tories, but there will be no golden era under Labour," he told a news conference in Liverpool. The TUC has published a new report, analysing the effects of possible public spending cuts on the 25 local authorities with the highest levels of unemployment. The study found that areas such as Liverpool, Leicester and Middlesbrough would suffer 40 per cent increases in unemployment. It also warned that a ten per cent cut in public sector staff would lead to 700,000 workers being laid off.