My 2p worth. I would rather be alive and lose a couple of seconds by not filtering up the left alongside an HGV, than be under his wheels and dead. I count myself as one of the riskier riders on the road in traffic, I will filter and probably do it too quickly, but I won't try and pass any vehicle on the left at a set of lights or a give way. This is the same as if I were driving, I would use my brakes if an oncoming vehicle was overtaking another and I thought they were not going to make it in time. It is just simple self preservation.