Martin Schulz, a former president of the European parliament, will stand in the German election

Britain could face an even more fervent pro-EU German leader in Brexit talks than Angela Merkel after Martin Schulz, the firebrand former president of the European parliament, emerged as her main challenger.

Mr Schulz blamed the Conservatives for reducing the UK to “rubble” by allowing the referendum. “The party of Churchill and Disraeli put its own interests before that of the country. Cameron, Johnson and Gove have left rubble behind them in a bid to fuel their personal ambitions,” he said in July.

As Britain negotiated its future relationship with the EU, Brussels would need to “defend the interests of its citizens, just as the UK will do”, he said.

Mr Schulz is to fight Mrs Merkel, 62, in September’s election as the Social Democratic