text: The prime minister has invited his German counterpart for a working dinner at his country residence, Chequers.
  The wide-ranging talks also cover the threat of so-called Islamic State, the situation in Iraq and Ukraine.
  Mr Cameron earlier welcomed Estonian Prime Minister Taavi Roivas to Downing Street for bilateral talks.
  The meetings with his European counterparts come on the day that a new campaign to get the UK to leave the European Union is being launched ahead of the in-out referendum, promised by 2017.
  Vote Leave, made up of Conservative, Labour and UKIP MPs and donors, says it wants to negotiate a new deal based on free trade and friendly co-operation.
  Mr Cameron has pledged to reform Britain's relationship with the EU before holding a vote on membership and will discuss his aims with Mrs Merkel as part of his continuing negotiations with European leaders.
  The pair will also discuss the migrant crisis affecting Europe, as European countries continue to struggle to cope with the influx of people reaching the continent from the Middle East and Africa.
  Russia's bombing campaign in Syria is also likely to be raised at the meeting, as concerns grow about Moscow's involvement in the war-torn country - as well as its backing for separatist rebels in eastern Ukraine.
  During talks with the PM at Downing Street, Estonian Prime Minister Mr Roivas thanked Mr Cameron for the UK's commitment to send 100 British military personnel to the Baltic region.
  Defence Secretary Michael Fallon has said the troops will deter Russian aggression beyond Ukraine and reassure eastern European Nato members.
  Speaking at a press conference on Friday, Mr Fallon - who held talks with his US counterpart Ash Carter in London - said the UK government was committed to building support for air strikes against IS in Syria.
  He said Russia's military action had made a "grave situation even worse".
  The UK is currently involved in coalition air strikes against IS targets in Iraq but not Syria, after Parliament voted against the move in 2013.
target: David Cameron is holding talks with German Chancellor Angela Merkel on Britain's EU reform aims, the situation in Syria and the migrant crisis.