I got my Brompton a year ago, and I ride it all year round. Initially I wore my normal work clothes, especially since I was doing fairly short journeys (about 2km at each end). In January I said: "I think it's important to avoid wind-chill by making sure that most of my skin is covered, even if it's only a thin layer of clothing." By May I was cycling in a T-shirt, then swapping it for my work shirt when I arrived at the office, but still wearing my normal trousers/boots on the bike. In June I started wearing lycra shorts and trainers to cycle, so I basically do a complete change of clothes at the office (although I tend to wear the same socks all day).
On the whole, this new approach is working well, particularly since I'm cycling a lot further than I used to (I average about 25 km/day). However, as I've got fitter I've found that I can do short journeys without sweating, so if I just do a 10 minute journey (e.g. coming home from an SJA class night) then I don't bother getting changed. I was up in Oxford in August, and I noticed that there are loads of cyclists around (including a lot of "traditional" bikes), but most people were wearing normal clothes to ride.
Now that we're moving into winter, it's starting to get a bit chilly on the bike. I'm now wearing gloves again, and I'm ok in T-shirt/shorts after I've warmed up. In fact, this may help by giving me an incentive to pedal faster - I hit a personal best when I came home on Friday evening (38 minutes from Balham station to my flat). The downside is that cotton T-shirts get quite damp, and then they get cold; also, I'm still exposed to the wind. So, I've now decided to invest in some extra clothing: bib tights and a long sleeved base layer. ("I need to buy some tights" is one of those phrases that I never expected to hear myself say!) I haven't tried bib tights/shorts before, so I'll be interested to see how they compare to the normal kind (with a waistband); hopefully they'll be a bit more comfortable.
Anyway, that leads to the main reason for this post: I'm not quite sure about the right order to wear these things. Do you put the tights on first, and then the base layer on top, or vice-versa? When I went snowboarding, I put the base layer on first, then put the "braces" for my trousers over the top; that makes sense, since the base is then the bottom layer. On the other hand, since you "go commando" in cycling shorts, it seems a bit odd to have something else in between on the top half of the body, and I've never seen anyone else cycling around with the shoulder straps visible, so that may be the equivalent of Superman wearing his underpants on the outside. I think that some people may have three layers (base layer, straps, jersey) but I don't have a jersey and I think I'll be warm enough without one. Admittedly, some people will probably think that I look stupid whichever way round I do it, but any advice welcome...
Which clothing goes on first?
Base layer then bib tights
Bib tights then base layer