Spent most of the afternoon fiddling with this. I'm convinced that the wxALIGN_CENTRE flag doesn't work.
I've written a little subroutine which does what I want; it's OK but it shouldn't be necessary
# centre_text( $text_control, $container );
# Not enough error checking, really ...
my ( $text_control, $container ) = @_;
my ($container_width) = $container->GetSizeWH();
my ($text_width) = $container->GetTextExtent( $text_control->GetLabe
my ( $text_x, $text_y ) = $text_control->GetPositionXY();
$text_control->Move( ($container_width-$text_width)/2, $text_y );