The foreign secretary is accompanying the Queen on her state visit to Nigeria.

The visit comes ahead of the opening of the Commonwealth Heads of Government Meeting this weekend.

Jack Straw will represent Britain at the event along with the prime minister and international development secretary Hilary Benn.

The royal trip is going ahead amid tight security following concerns about a possible terror attack.

The Queen will formally open the summit on Friday with observers predicting a difficult meeting which could be split along racial lines.

However Tony Blair has denied that the threat from president Robert Mugabe to withdraw Zimbabwe from the Commonwealth will drive a wedge between Britain, Australia and Canada on one side and African states on the other.

"I don't think it will split the summit, I think people will note the present situation and move on, and what the Mugabe government decide is up to them," the prime minister said in Downing Street on Tuesday.

"I just think it is a tragedy for people in Zimbabwe that as a result of the actions of that government that people suffer so much there, and the people that are suffering, the vast majority of them are the black population that are suffering."

Nigerian president and summit host Olusegun Obasanjo deliberately failed to invite Mugabe to the gathering with Zimbabwe currently suspended from the group.

Trade issues could also dominate discussions with the Commonwealth hoping to come to an agreement which could provide some momentum towards re-starting the stalled World Trade Organisation talks.

Ahead of his trip, Blair met with leaders of Caribbean countries to discuss trade between the West and the developing world and other Commonwealth concerns.

And Obasanjo said at the start of the week that the unusual make-up of the Commonwealth made it a good forum for debate.

"We've rich countries from the West, large developing countries like India and smaller countries, as small as Caribbean islands," he told journalists.

"If we can agree, such agreements can persuade others. The Commonwealth is unique in this respect."

Blair has been accused of snubbing the event after it was reported he will leave the summit early in order to host a reception for the English rugby union team following its world cup victory.

However speaking at prime minister's questions on Wednesday he insisted he was "coming home early for a private appointment of a different nature altogether".