The underlying reason for the decline is down to the banking system going into meltdown and loss of confidence.
Which is why this is such a load of hot air on the part of the, errrm, experts. There is very little fundementally wrong with the UK and European economies. The US has less influence than once it did. The banks will have to relax thier lending criteria soon or they will start to hemorrhage real money, then their priorities will change. In the not too distant future we'll wonder what all the fuss was about.
Anyway, the current slow down is probably beneficial in the long run, permits a degree of introspection and will probably help some of the Asian economies which are accelerating too quickly too.
As W H Auden suggests, probably better to be a "rider" than a "reader".