Clegg, welcoming the delegation to Downing Street at the start of a four-day inspection visit, said the new coalition government shared the previous Labour administration's commitment to the bid.
England, who lasted hosted the World Cup in 1966, are competing against Russia, the United States, and joint bids from Portugal/Spain, and Belgium/Netherlands to stage the finals in eight years time.
Football's governing body will announce the host nation on December 2 in Zurich.
"I believe this is an exceptionally strong, unbeatable bid. We in this government believe in it, we hope that you will believe in it," Clegg said in a welcoming address.
"There is a relatively new coalition government in the United Kingdom and we want to emphasise to you that the commitments, the declarations and the guarantees provided to you by the previous government are ones that we back 100 percent.
"One of the first things we did when we created this new coalition government was to write into our founding coalition agreement our resolve to back to the hilt the England 2018 bid."
The coalition between Clegg's Liberal Democrats and the Conservatives of Prime Minister David Cameron, who is on holiday, was formed in May after no party won an outright majority in parliament after a general election.
One of the selling points of the England bid is its commitment to legacy projects for the international development of soccer.
Andy Anson, CEO of the England bid, said it would "focus on what we can do for football all over the world."
England were given a boost earlier on Monday when FIFA President Sepp Blatter, speaking in Singapore, told Inside World Football:
"The easiest way to organise the World Cup is to go to England. Everything is there -- fans, stadiums, infrastructure - it's easy."
But, he added that Russia, seen as England's biggest challenger, was a strong candidate.
"You cannot deny Russia if they bid for something. They are more than a country. They are a big continent, a big power."
Harold Mayne-Nicholls, chairman of the FIFA delegation and president of the Chile FA, told Clegg: "We will gets answers to all the doubts we have, study all the documents and we will work hard with the local organising bid committee to provide a very fair and objective report for the FIFA executive committee members.
