Will I be hot?
Will I be hot in London in January?
Verdict
No — No, comfortable.
Highs cap at 46°F — no heat-management gear needed.
Day vs. night
Day
46°F
Cool
Sweater weather with the option to add a light shell.
Night
36°F
Cold
Cold enough that a hat and gloves become mandatory.
Why
London in January averages highs of 46°F, lows of 36°F, 12 rainy days.
Temperature is comfortable across the day; pack for style and weather resistance, not heat management.