My reading of it is that passing through a UK port means I enter a legal limbo. If stopped by an inquisitor, I'm likely to assert my right to silence. This may mean I'm detained and intimidated for 9 hours. At the end of this I can be arrested and charged with 'non-cooperation', this may involve further detention and/or fines all for simply remaining silent.
Leaving the UK is worse, as I'll likely miss my flight, and have the expense of re-booking.
This is just if the border agents are acting within 'the law'.
Virtually every UK citizen passes through a port at sometime during the year - the inquistors can simply wait there for anyone they are interested in. It effectively means the right to silence is dead.
Foreign visitors should be aware they can be legally forced to give up their Gmail/Facebook passwords. Hope Big Ben is worth it.
I wonder what the plans are for Julian Assange when he eventually leaves the UK - almost certain to be detained under Schedule 7.