WBI is what is called the NudeOScope here, as opposed to the more common outside the US/UK WTMD. You'll want to read up on that as many here choose to opt out of the WBI but there is no opt out option in the UK if you are selected. It is the scanner which may expose you to harm, and which shows more than you may wish to reveal about yourself.

Chances of being asked to show your laptop to customs are very slim, so don't get too worked up about it. Are you thinking of security, or of customs? Laptops are generally to be removed from the carry on for security, but most times customs doesn't ask to see them.

You should be able to check your luggage all the way through, but may need to pick up your onward boarding pass in LHR. 2 hours should be fine for all of that.