Clinton will discuss the language of diplomacy

A massive security operation surrounds Mr Clinton's visit to the 10-day event, hosted every year by the mid Wales border town which has a population of just 1,300.

Secret Service agents and the Metropolitan Police have been aided by Dyfed-Powys Police to put strict measures into place after he decided he would like to stage a walkabout in the town to meet visitors.

Mr Clinton - who is reported to command at least $100,000 per speech - will talk about conflict resolution and the language of diplomacy when he appears at the BBC Wales World Lecture on Saturday evening.

He will be carrying out his first public engagement in the UK since ending his presidential term.

Poetry book

Organisers say they could have sold the 1,300 tickets costing �100 several times over.

It has been estimated that his presence at the festival will bring an extra �1.5m into the area.

Authors booked to appear this year include Louis de Bernieres, Margaret Atwood, Nick Hornby, Germaine Greer and Frank McCourt.

Sir Paul McCartney, who has recently published a book of poetry, will also be at the festival which attracts crowds from across the world.

Van Morrison is making a return visit to Hay

Pop band Pulp kick off the festival on Thursday and Irish rock star Van Morrison is due to perform on 1 June.

As a result of nearby foot-and-mouth disease outbreaks, the festival has been moved from its usual farm site on the outskirts of Hay to a less sensitive site in the town centre.

"We are expecting that there will be a certain number of people who will feel cautious about coming to the countryside, but we have been able to move the festival into the very centre of Hay-on-Wye," said organiser Peter Florence.

Hay-on-Wye is a small market town in the Black Mountains of mid Wales which has made a healthy business of its 39 bookshops and its 14-year-old famed festival of language and ideas.

The organisers of the festivals are boasting of "tens of miles" of book shelving to browse.