Since no-one else has mentioned it - thought I'd add, that in slow moving two-lane traffic, like in the mornings heading into the city - there is a long A road (A610) which has 2 lanes of traffic which mainly does 0-10mph, I tend to travel between the two lanes of traffic. I find this gap is OK, there is little lane changing, I am (so far) never caught out by cars in the wrong lane - as if they are they tend to have to signal for a while, and move very tentatively. There is no issue with peds - as they are not dappy enough to cross 4 lanes of traffic where there isn't a crossing (as there are plenty of crossings, and invariably the other lanes are much quieter and therefore much faster moving traffic).
I duck into the left lane when I'm going the same speed as the traffic, and preferably behind a lorry or something that offers a bit of drafting opportunity!
Generally the middle gives me a lot more room than the left (even where that would be a "safe" option: no parked cars, no drives or roads on the left, stationary traffic), and is better than facing 40mph cars head-on.... I don't like the central islands - which cars get too close to for me to go through normally. And I'm not a fan of going the "wrong way" around central islands....