Mexican president Enrique Pena Nieto vowed to strengthen the rule of law on Tuesday in a visit to Britain aimed at bolstering a national image battered by crime and corruption.

The trip comes as Pena Nieto struggles with drug violence and falling approval ratings at home, after the disappearance and alleged slaughter of 43 college students by a police-backed gang sparked international outrage and protests.

"Our democracy has not been without difficulties," Pena Nieto told the House of Lords, the upper house of the British parliament. "In the recent past, we have experienced painful moments for the acts of barbarism committed by organised crime."

"These criminal acts have made clear that we must continue to strengthen the rule of law."

Pena Nieto was welcomed with a banquet hosted by Queen Elizabeth II at Buckingham Palace, where he and his wife Angelica Rivera are staying until Thursday.

The president arrived at the palace in a carriage with Queen Elizabeth, 88, and was greeted with a canon salute, a royal guard and a band. But Mexicans in the crowd expressed scepticism about the trip.

"The visit can improve our image abroad, but it cannot fix Mexico," said Hector del Castillo of Mexico City. "There is violence, the country is sad."

Over 100,000 killings and disappearances have occurred since the government of Felipe Calderon declared a "war" against drug traffickers in 2006, and Pena Nieto admitted to the Financial Times to a climate of "incredulity and disgust" on the eve of the trip.

A protest of about 150 young Mexicans outside the office of Prime Minister David Cameron called on Britain not to turn a blind eye to Mexico's "human rights crisis" ahead of the visit.

Some with their faces painted like skeletons from the Mexican Day of the Dead, the crowd chanted "Mexico! Justice!" and counted to 43 out loud, to remember the students that went missing in the southern state of Guerrero in September.

A woman who gave her name only as Patricia, for fear of reprisals, said her nephew had been shot dead by police in Guanajuato in central Mexico but that nobody had been held accountable."I'm really upset that the red carpet has been rolled out for this gangster," said the businesswoman. "It's embarrassing for the UK people to receive this cartel guy in such a way."

Laura Morales, a 32-year-old immigration adviser, said that human rights were more important than business or trade links.

"We the Mexican community believe that it's very important that the British government demands an explanation when it comes to the human rights crisis going on in Mexico," Morales said.

A spokesman for British Prime Minister David Cameron said that concerns over the situation in Mexico would be raised with Pena Nieto "in the spirit of collaboration" during the trip.

"You can expect the prime minister to raise concerns that have been made and have arisen with regard to human rights for example in the judicial system in Mexico," the spokesman said.

Pena Nieto is to meet with Cameron on Wednesday, and will travel to the centre of Scotland's oil industry in Aberdeen on Thursday to sign an agreement with companies that extract oil from the North Sea. AFP