Cameron: Welfare reform to be 'absolute requirement' in EU deal

He noted that "under the [EU's] free movement rules, national welfare systems can provide an unintended additional incentive for large migratory movements".

According to the BBC, Cameron is keen to be allowed to refuse in-work and out-of-work benefit payments to new migrants for four years after they enter the UK.

He is also wants rules on voting on single market issues to be altered so London cannot be outvoted by eurozone members acting in a bloc.

Cameron's wishlist depends to a large extent on the willingness of his EU partners to accommodate London. But London has leverage as countries such as Germany do not want Britain to exit the EU when it holds a referendum on any new 'settlement' by the end of 2017.

He will see his fellow EU leaders at a summit in Riga on Friday (22 May), where he's expected to have preliminary informal talks about his plans before a major EU summit in Brussels in next month.

Treaty change?

While EU diplomats say there is no appetite for a treaty change in member states - and it would be all but impossible to achieve one in such a narrow timeframe - other routes are being looked for.

These are "models that not require treaty change straight away", said one EU diplomat.

These include the Danish or Irish solutions - a kind of promise to incorporate agreed changes into later treaty modifications. Copenhagen secured Danish opt-outs in four areas after it rejected the Maastricht treaty in 1992. On the back of the promised opt-outs, it then backed the treaty in a second referendum the following year.

When Irish voters first rejected the Lisbon treaty, the government secured 'guarantees' on corporate tax, social issues and neutrality. Ireland then voted in favour of the treaty in 2009.

New EU labour mobility package

EU officials are also expecting London to shape labour mobility legislation - due to be tabled by the end of the year by EU social affairs commissioner Mariann Thyssen.

The commission has already specifically said the measures will tackle "abuse by means of better co-ordination of social security systems".

Cameron's drive to secure some concessions from the EU have already received a boost from Berlin.

In an interview with the Wall Street Journal and Les Echoes this week, finance minister Wolfgang Schaeuble said he would help the British leader to secure EU reform so long as it included strengthened economic governance of the eurozone.

He said he had spoken with UK finance minister George Osborne "about how we can combine the British position with the urgent need for a strengthened governance of the eurozone, which is something the British government also agrees is necessary".

Schaeuble also noted that Berlin has a "huge interest in the UK remaining a strong and engaged member of the European Union".

Meanwhile Cameron's broader speech on immigration included a series of proposals to curb immigration by making Britain "a less attractive place to come and work illegally".

These proposals include make illegal working "a criminal offence in its own right" and tracking people considered to be in Britain illegally by doing more checks on expired visas, making sure banks "take action against existing accounts held by illegal immigrants" and changing rules so "landlords can evict illegal immigrants more quickly".

These measures are to be set out in a new immigration bill next week.