David Cameron is travelling across European countries in an attempt to intensify his lobbying of EU leaders over his plans to renegotiate the terms of Britain's EU membership.
The Prime Minister has embarked on a two-day tour of four European capitals. First meeting Prime Minister Mark Rutte of the Netherlands, he will then meet French President Francois Hollande. This will be followed by meetings with Polish Prime Minister Ewa Kopacz and German Chancellor Angela Merkel.
We have a clear set of requirements. The prime minister is very clear in dealing with European Union counterparts - that if we are not able to deliver on those big areas of concern that the British people have we will not win the referendum.
And we expect our European Union partners to engage with us in delivering a package that will enable the British people to decide that they think Britain's future is best delivered inside the European Union.
Mr Hammond added that the UK expected to secure a "substantive package of reforms" as the talks began, while warning that the government would "rule nothing out" if Europe fails to act.
Other demands involve the UK's sovereignty. The Prime Minister is expected to negotiate for an opt-out from the "ever closer" union; to give national parliaments the right to join together to block new legislation; and to ensure that non-Eurozone countries could not be forced into changes to the single markert rules by their Eurozone counterparts.