Keep them in the brightest light possible, which usually means as close as possible to the window.
Normally in London area, Wisteria are grown outdoors all year round. They are fully winter hardy in your climate. However it takes a seedling or a more mature plant of Wisteria time, about 2 months of steadily lower and lower night time temperatures to develop full winter hardiness. This means that it is too late in the year to just pop your seedlings outside for the winter.
Normally, we don't start seed indoors until after the middle of winter has passed.
Young seedlings can often pull through a winter on a window sill or in an under lights set up without bad effects. Mature trees will often have problems if not given a cold winter rest. But seedlings tend to not have much trouble. Your seedlings should be fine. In spring, put your seedings outside after danger of frost has passed, then never bring them inside again, except for a few hours at a time to display for guests or to take photos. Actually a day or two indoors most of the time is not a problem, but they really are an outdoor species.
