For those advance footsoldiers of Chris Coleman’s red army trading Sussex for Aquitaine yesterday morning there was only a sense of possibility. As Gatwick disappeared under cloud the talk was of Gareth Bale and Aaron Ramsey, and tomorrow’s opening match here against Slovakia, Wales’ first in a major tournament since 1958.

Similar feelings are being evoked as fans leave Northern Ireland, another making their European Championship finals debut, and Iceland and Albania, who have not previously played in any major competition. For others, however, particularly those charged with hosting the event, but also those who paid to broadcast it, and the wider community of football supporters, there is trepidation as well as expectation. Every football tournament begins with a mix of these moods, but Euro 2016 opens tonight with a surfeit of both.

The expansion of the tournament has enabled supporters usually left disenfranchised to enjoy the thrill. But there is also risk, much more so now than when decided, five years ago.

The initial fear was expansion, to an unwieldy 24 teams, would dilute the quality of the football and lessen one of the European Championships’ special features - its unpredictability. Now there are darker fears. With 51 matches in 10 venues to secure, and 24 teams to protect, the French security forces will be stretched as they seek to avoid a terrorist outrage. Less threatening, but still with potential to seriously disrupt the tournament, are the wave of strikes convulsing France. Uefa, French president Francois Hollande, and everyone else will be mightily relieved if,  come July 11, it has passed off safely and smoothly.

It is to be hoped by then the main topic of discussion will concern the football, and whether expansion was justified. The first time England qualified for this event, in 1968, four nations were involved and even with the final replayed the competition was done and dusted inside a week. This summer’s edition will last a month, nearly twice as long as the Olympics.

The steady growth of Uefa’s international flagship is partly due to a corresponding rise in eligible nations. With the break-up of the Soviet Union and Yugoslavia, expansion eastward to Azerbaijan, and incorporation of makeweights such as San Marino and Gibraltar, a record 54 nations entered - against 31 in 1968.

But this latest increase is primarily due to football politics. To win and retain his presidency of Uefa, in which each country has one vote, be they Germany or Liechtenstein, Michel Platini courted the smaller nations by opening up qualification to both the Champions League and European Championships. Platini has since been drummed out of football administration in disgrace, but this is one of his legacies.

The next month may aid his rehabilitation, or further condemn him. While enlargement means there are fresh elements 24 is a difficult number for a competition that progresses to knock-out stages. The traditional group-stage method of qualifying two from four results in 12 teams. And then what?

Fifa struggled to find a satisfactory solution when the World Cup was the same size, from 1982-94, eventually settling for qualifying the four best third-place teams. The Euros have followed suit, which has two consequences. It reduces the tension and meaning of the group stages as even a moderately decent performance from the big nations should be enough to qualify - unlike in 2004 when Spain, Italy and Germany were all knocked out after coming third in the group stage. It also significantly extends the duration. This tournament will take 36 matches and 13 days merely to get the the last 16.

While Leicester City have underlined there are always exceptions the longer a tournament progresses the less likelihood of a surprise. The traditional nations have more squad depth and are therefore less affected by injuries and fatigue. The short format of the Euros has previously encouraged the unexpected with Czechoslovakia (1976), Denmark (1992) and Greece (2004) among previous winners. Indeed, more different nations have won the Euros, which have only been held 14 times and are restricted to one continent, than have shared the 20 World Cup tournaments.

Unsurprisingly few are expecting a shock this time. L’Equipe, the French sports daily, canvassed a former player from each of the 24 nations yesterday. Asked to name their favourites (several, in some cases) 17 chose France, 11 Germany, nine Spain. Belgium, the best known dark horse since Black Beauty, was next, with five backers. The only ex-player to vote for anyone else was Andriy Shevchenko who named Germany, Spain and France, plus, perhaps with a nod to previous employers, Italy and England [The English jurist, Chris Waddle, chose Spain and tipped England for the quarter-finals].

However, it is unlikely to be so clear-cut. The movement of players across Europe has led to a broadening of the talent base and there will be few teams without one to watch and savour. Cristiano Ronaldo, Zlatan Ibrahimovic, Robert Lewandowski and Bale are four of the very best, but none play for play for the traditional powerhouses. Nor do Luka Modric, Arda Turan, Granit Xhaxa, David Alaba or Petr Cech. Most teams are capable of an upset - England and Wales would be wise not to underestimate a Slovakian team in good form with skillful players -  and, as the Dutch discovered in qualifying, reputation counts for nothing if a team is disorganised.

The Dutch will be missed, but this still has the potential to be a fine tournament if managers and players approach with a positive attitude. The best Euros for qualify football were probably 1984 and 2000. Both were won by France, which may not be a co-incidence. As with rugby union, when they are good, they are very good. The onus is thus on Les Bleues to set the tone tonight. It is another responsibility for the host nation. For the sake of the tournament, the players and fans, one hopes their shoulders are broad enough to carry the burden and make Euro 2016 one to remember for the right reasons.