@shaunc
"To say 'England [is] on the attack' would infer the country of England as a whole was on the attack. England as a country is not on the attack, but a team of players representing England are on attack."
The context where this phrase is being used is a football game. In this context, it can be assumed that saying, "England is on the attack" is referring to the English national football team, and not the English military. For example, if one was to hear, "England is on the attack" on the local news, one would assume that the English military is attacking another country.
Using YOUR logic, saying, "England are on the attack" during a football broadcast would infer that the individual citizens of England were on the attack. This is obviously not the case because that interpretation would be completely out of context.

That said, I agree with what providencejim said. I believe that the base of this confusion is a cultural difference between the US and the UK. I am an American and I have always found the usage of plural by the British very odd. In general, I find that football teams are ambiguously named: Birmingham City, Manchester City, Barcelona, Real Madrid, Aston Villa, Inter, Milan, Ajax, etc; compared to American football teams: Chicago Bears, Atlanta Falcons, Jacksonville Jaguars, Miami Dolphins, San Francisco 49ers, etc. This is the key to the discrepancy. When Americans want to refer to an NFL team as an organization we use the city and when we want to refer to an NFL team as the collection of players, coaches, and fans, we use the team name. For example, “Chicago is beating Green Bay” and, “The Texans are doing well this year.” Since football fans across the world generally only have one name to choose from, they say, "Birmingham are" and, "Birmingham is" based on the desired usage. I don't understand why the British and others INSIST upon using the plural even when the singular should be used. My only explanation would be either habit or stubbornness, or both. I recognize that there are times when a team should be referred to as a team of players, coaches, and fans, yet there are also times when a team should be referred to as a single entity.