I've noticed a number of posts recently saying you must check your blind spot every time you change lane on motorways and rather than derail those threads thought I'd post a new one.
When people say check your blind spot, what exactly is meant? A proper look behind or just a quick glance to the side?
My personal thoughts: if you're using mirrors correctly on the motorway you should have a very good knowledge of what vehicles are around you, so if you've seen a vehicle approaching from behind, it hasn't passed you and you can't see it then you should already know it's in your blind spot. Additionally, a vehicle is big enough that if you can't see it in your mirrors it's probably up to your shoulder anyway, so a very quick glance 90 degrees left or right will show it. I get very twitchy about turning to look back and doing a full blind spot check - apart from anything else you inevitably won't keep going in a straight line when you twist your body. I'd be interested to know what other people do/think.
(Obviously, if in any doubt, check!)