An interesting article from the BBC, here.
We had recorder lessons at school, like most people of my generation, I think. I quite enjoyed it and, by the time the lessons stopped, could read music at a basic level. That must have been when I was about ten years old. Between the ages of 11 and 13 or so, I had private trombone lessons, which I tried hard at, but found hard to get in to.
Then, when I was 16, I started playing around with a little toy guitar we had at home, taught myself some chords and started enjoying music properly for the first time. Sadly, rock stardom passed me by, but I did have a great time in my late teens playing in my own band at a few pubs, as well as jamming away at university. Nowadays, thanks to another small toy guitar I bought (a small one being more practical to take to parties, the beach, etc) I find myself playing on a daily basis for my own - and occasionally other people's - amusement.
This experience has lead me to believe that it's the guitar that should be taught as a group instrument at school, or as the instrument that parents encourage their kids to learn when they're young.
To enjoy playing the piano to any reasonable degree takes a lot of solitary effort. To enjoy playing the trumpet, trombone of violin takes similar amounts of time and dedication. More importantly, to get to a level where you can make some nice sounds takes real talent.
The guitar, on the other hand, doesn't need a huge amount of musical sophistication to reach a level where you can bash out a few basic pop songs. This is important - the child learning the guitar starts to enjoy the process a lot more quickly, doesn't need to be part of a huge orchestra or group to do so and is able to play the sort of music they like. The guitar's also a lot more practical to carry around than a trombone, piano, or even a violin.
After several months learning the trombone I could play some Hungarian folk songs rather badly. After a week of mucking around on the guitar, with nothing but a book of chords to guide me, I could play some simple versions of Bob Dylan, the Beatles and so on. I expect today's books would have the chords to more recent pop tunes. Nowadays I couldn't play a Hungarian folk song on the trombone to save my life, whereas even someone who picks up a guitar after not touching one for a few years can quickly start to play something decent again.
All of this suggests to me that having kids learn the guitar during school music lessons will get the average person enjoying music, whilst those with talent can easily more onto something more sophisticated. Britain could become a nation where every man and woman would be able to play the riff to Smoke on the Water - that would be quite a cultural leap forward.
The next question, of course, is whether government schools in Britain even have music lessons any more, but that's an entirely different topic.