"Roland Perry" wrote:
"From 2 January 2011, the minimum balance on your Oyster card before it is
automatically topped up is changing from £5 to £8. This is to ensure that
all customers with Auto top-up will always have enough credit on their
cards for any journey they wish to make."

Slightly misleading original subject line though - this is in relation to
*Auto* top-up, and is not to be confused with the £5 minimum top-up rule at
Tube station ticket offices (which seemingly isn't always enforced).