Many thanks for that Rob. I must be an idiot! I didn't realise the 3-way slide option was INSTEAD of a PIN number - I thought the slide option was automatic and sliding to the unlock position took you to the PIN screen as it did first time after the update. I didn't realise you could have security OR slide but not both!
I should have realised - I spent a while wondering how you could access search and camera without the need for a PIN if you needed a PIN to unlock, but concluded it was limited access!
Thanks again both.