The European Parliament's president has taken a tough stance on proposed reforms to Britain's relationship with the EU.
Martin Schulz told ITV News Deputy Political Editor Chris Ship a deal on EU reform which caters "to narrow self-interests" will meet with resistance from the EU's Parliament.
He added that many of his colleagues had told him "if the Brits want to leave, let them leave".
EU Parliament's @martinschulz is in town: Currency of the EU is the Euro/Britain tests our patience/MEPs will not tolerate discrimination
On Cameron's "multicurrency union" @martinschulz says 'The currency of the European Union is the Euro. The Treaties are very clear on this'
Addressing David Cameron's negotiations for changes to migration rules within the EU, Schulz said solutions cannot come "at the price of discriminating against EU citizens".
Mr Schulz spoke before delivering a lecture in London on the EU.
David Cameron is expected to warn that voting for a "Brexit" would result in refugee camps springing up across the south-east of England.
If voters chose to stay - whenever the referendum comes - the deal upon which that decision was reached may not be the final word.
As his tour of Europe gets underway, David Cameron faces a fight to stop his proposed EU deal being watered down further.