European Parliament President Martin Schulz has said that although, "a strong supporter of the UK remaining in the EU, Britain often tested the "patience and goodwill" of other EU member states with its "continuous demands."
In a wide-ranging speech at the London School of Economics on Friday, he said, "I believe we need the UK to make the EU stronger and better. And to make something stronger and better sometimes it's necessary to push hard and be critical. When the UK says it wants to make the EU more democratic, more transparent, more competitive and less bureaucratic - I am in."
Nevertheless, he took issue with several of UK Prime Minister David Cameron's renegotiation demands, and with European Council President Donald Tusk's draft response to them. Schulz warned that, "proposals which cater to narrow self-interests, risk undermining the common good, or would set dangerous precedents for a Europe à la carte will meet with resistance from the European Parliament."
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He was especially critical of the 'multicurrency union' requested by Cameron, saying, "The currency of the European Union is the Euro. The treaties are very clear on this. And the treaties also guarantee an opt-out for the UK. There is simply no need for further clarification."
"However, there is a need for clarifying possible de facto veto rights due to ambiguities in the present texts. Giving a de facto veto to any member state in the European Council on Eurozone issues is unacceptable for the European Parliament - such a step would entail the risk of paralysis for the Eurozone."
Welfare payments, one of the most controversial elements of the renegotiation proposals also came in for criticism from the German MEP, with Schulz arguing that the so-called 'emergency brake' mechanism being offered to David Cameron to resolve his request for a ban on in-work benefits for EU migrants living in the UK, would create significant inequalities among EU citizens.
"If there are indeed EU citizens coming to the UK more for the benefits system than work opportunities this needs to be addressed. But solutions cannot come at the price of discriminating against EU citizens. This is a fundamental principle of our Union."
"Let me to say this very clearly: the European Parliament will support all proposals which fairly address real problems which may emerge from free movement - as long as they do not cause discrimination and undermine European values."
The German MEP warned that Brexit victory would risk triggering a second Scottish independence referendum, a drop in foreign investment and would damage London's status as a leading financial centre.
"Let's face it: a huge chunk of London's attractiveness for global finance is down to it being part of the internal market. And as often said by the UK Government, a strong, sound and resilient Eurozone is an advantage for the UK."
"The UK has one of the most open markets in the world - this is great, it's the foundation of your wealth. But it also makes Britain very vulnerable to global economic and financial crises and to the volatilities of global markets", he added.
"Isn't it reassuring", he said," to be part of the biggest single market in the world? Being part of a big bloc makes countries more resilient against external shocks - and less vulnerable to the volatilities of global markets. Britain does half of its trade with the EU. Leaving the EU would be bad for pay and jobs. While staying in is good for prosperity and security. Some things are as simple as that."
EU heads of state will discuss the UK settlement deal later this month at their summit on 18-19 February. An agreement at that meeting would pave the way for a British in-out referendum in the early summer, potentially on Thursday June 23.