Obama visit: How special is the UK/US relationship?

When President Obama and David Cameron hold their formal talks in Downing Street on Wednesday, they are likely to focus on hopes for progress in the Middle East following the president's recent initiative and the ongoing conflict in Libya.

Mr Obama is then expected to provide more details in his address to both Houses of Parliament and to explain how he sees the state of relations between the US and the UK.

Mark Mardell is travelling with the presidential group and sent this report.