Filtering up the left is legal but I’m vary wary of it. Drivers just aren’t as aware of what’s on their left and passengers have no idea, if you go up the left be wary of people getting out of the car and left turners.
I wouldn’t be surpried if some of the car drivers that pull right over to the curb are letting you round the outside, if there is a bike (motorised or pedal powered) behind me in a queue I always pull to the left if they’re in the middle of the lane to give them a safe route up the middle. Some of them are bound to be cocks though.
My advise is the best way to filter is up the middle if possible, and only if it’s safe. No point racing to the front of every set of lights if the same people are going to have to get straight back past, it’ll just piss them off and you’ll have more chance of getting run over.
And never, ever, ever, ever, ever wait infront of the back of a big vehicle, and only wait infront of it if you know for sure the driver can see you, give them a nod or something to check.