The president of the United Arab Emirates has been given a lavish welcome as he was greeted by the Queen on the first day of a state visit.
Sheikh Khalifa bin Zayed Al Nahyan was taken on a carriage procession with the Queen to Windsor Castle, where he was given a guard of honour.
The state visit comes amid claims that three Britons were tortured in Dubai before being jailed on drug charges.
Prime Minister David Cameron will meet the president on Wednesday.
Mr Cameron has said he will raise the case of the imprisoned Britons, who were jailed for four years each.
The prime minister was at Windsor Castle on Tuesday for a state lunch for the president, hosted by the Queen. Among the other guests was the UAE's deputy prime minister, Sheikh Mansour bin Zayed Al Nahyan, owner of Premier League football club Manchester City.
Tunics and bearskins
In a speech, the Queen told the president: "Our two countries have been close friends since before the foundation of the United Arab Emirates in 1971, under the wise guidance and leadership of your late father, Sheikh Zayed."
She added: "The UAE is one of our largest trading partners in the Gulf region, and we have welcomed Emirati investments in the United Kingdom in many areas from the construction of the largest port facilities in the UK to the Emirates Skyline, the spectacular cable-car crossing over the Thames and, of course, Manchester City."
The president had earlier been treated to a welcome of pomp and military splendour.
He enjoyed a carriage procession with the Queen through Windsor to the castle where guardsmen from the 1st Battalion Welsh Guards in their scarlet tunics and bearskins formed a guard of honour.
The visit helps build on the relationship between the two countries, which have a growing partnership in defence and security
The UAE represents Britain's largest export market in the Middle East.
President Al Nahyan's state visit follows one made by the Queen and the Duke of Edinburgh to the UAE in 2010 and a visit there by Mr Cameron in November.
The president's late father, Sheikh Zayed bin Sultan Al Nahyan paid a state visit to the UK in 1989.
Annual bilateral trade between the UK and the UAE now exceeds £10bn. More than a million Britons visit the UAE each year.
A squadron of RAF Tornado jets is based at Al-Minhad, a discreet and well-guarded airbase south of Dubai, which is one of the seven emirates which make up the UAE.
The BBC's security correspondent, Frank Gardner, says millions of pounds have been spent by the UAE upgrading the base, which will soon serve as a vital staging post for the withdrawal of British combat forces and their equipment from Afghanistan.
On Monday, east Londoners Suneet Jeerh, 25, Grant Cameron, 25, and Karl Williams, 26, were found guilty of possessing synthetic cannabis in Dubai.
The men say they were subjected to torture by police, including electric shocks and beatings.
Police in Dubai have denied any wrongdoing and say an internal investigation into the torture allegations found no evidence to support the claims.
Legal rights charity Reprieve has taken on their case and, in an earlier letter to the campaign group, the prime minister wrote: "We continue to press for evidence for a full, impartial and independent investigation into the allegations.
"The absence of an independent medical examination remains a concern.
"During the state visit of His Highness Sheikh Khalifa bin Zayed there will be opportunities to raise a wide range of issues including concerns about this and other consular cases."