In reply to Trangia:
I've just done two weeks of jury service and smart casual is indeed the appropriate wear. "Your Guide to Jury Service", which is sent to every juror when first summoned, spells this out clearly: "It is suggested that you dress comfortably. You should as you will be sitting down for a long time. There is no strict dress code, but you should dress appropriately."
Most of the jurors turned up in smart casual dress, suitable for an office job. I wore smart trousers, shoes and shirt. Three of us on the last jury panel I was on wore ties, which is unnecessary. No one wore jackets; most took light sweaters, which is practical, because the assembly area and court rooms may feel variously a little warm or a little cool. No one wore flamboyant clothing. The best dressed lady was an immaculately dressed muslim student with elegant head scarves.