Nick Clegg has joined what the shadow home secretary Yvette Cooper calls an "arms race" on immigration. Although he warns David Cameron against caps on EU migration levels, or any sort of quota system, he is in support of curbing benefits to EU migrants.

He appears to be making his views known ahead of a big speech on immigration the Prime Minister is planning for this week. And while part of his intervention serves as a caution for the Prime Minister, there is also an element of support for a tougher stance in his claim that benefits should be curbed for EU migrants.

However, Cameron could be relying on harsher welfare rules as the backbone of his upcoming announcement, considering the free movement of workers question is harder to solve when not campaigning to leave the EU, which means Clegg is pre-empting his plans a bit. What also takes the shine off Cameron's imminent speech is that Labour has also laid out very strict proposals concerning benefits to immigrants, with shadow work and pensions secretary Rachel Reeves' plan to delay benefits for EU migrants for two years (the current system is three months).

In an article for the Financial Times today, Clegg lays out his view that caps or quotas would put the UK in "the worst of all worlds":

Ukip will say it is not enough. Europe will say it is not possible. Once again the British people will be plunged into a cycle of wild overpromising and inevitable disappointment, their scepticism confirmed. And the risks to the openness of the British economy will be considerable.

Clegg goes on to describe the Tories' doomed aim of bringing net migration levels down to the "tens of thousands" as "a foolish target we warned them they would miss".

This is a direct message to the PM, in which Clegg claims he will be unable to curb the number of EU migrants entering the UK, and that it is an undeliverable promise. This is also Ukip's argument; it sees the only chance to do this would be leaving the EU. Clegg, in contrast, argues that it would not be sensible or beneficial for the UK to control its borders with the EU in this way, for the sake of British business. The newspaper in which he chose to write this piece is a telling choice.

However, Clegg has joined Labour, and stolen a march on the Tories, by proposing even stricter rules regarding EU migrants claiming benefits. This is now another area of policy overlap for the Lib Dems and Labour, as observers continue to predict what a coalition, or some form of alliance, would look like between the two parties following the election.

Unlike the other main parties, however, Clegg is at pains to emphasise that, "overwhelmingly, European migrants come here to work and pay taxes", something I have covered extensively in recent weeks, as well as the myth that Britain is more generous to immigrants than its EU neighbours are. But Clegg nevertheless proposes new ways to curb handouts to migrants: