Sorry this is long! I haven't been for a while, so some details might have changed. What day/s of the week are you visiting? These aren't specific Christmas pop up markets but locals markets which are there all year round. If visiting on a Sunday, 1 idea:
-Get out at Liverpool Station. Walk through Spitalfield markets- bespoke/new items from soap, clothing, hats, food, cards, trinkets and more
(An alternative is to miss Spitalfields markets and get out at Shoreditch High St overground instead of Liverpool st).
-Walk to Bricklane markets. Parts such as the 'UP markets' are new/bespoke made items. Some parts have antiques, vintage. The further towards Bethnal Green rd you come, they have more 2nd hand items, fruit/veg stalls, flea market type in the side streets.
-Grab a salt beef beigel at 'Beigel Bake' on Bricklane. There is another beigel shop 2 doors down, but this is the better one IMO. There can be a queue out the door on busy days, but it does move quickly! Also pick up their cheesecake and carrot cake to take home 😋
-Walk further to Columbia Flower Market. The centre of the market can be very crowded. If its too busy, walk behind the stalls on the pavement. At Christmas, there will be Christmas trees, mulled wine, Christmassy pot purri etc for sale in addition to the regular bulbs, plants, flowers. There are also lots of independent shops along the road, other than the flower/plant market.
After that:
-If you have children with you, the V&A children's museum isn't too far to walk from there and its free. Yards from Bethnal Green tube. www.vam.ac.uk/young?srsltid=AfmBOopOtA_Sb8nTkGOxzWPeFera79u4s12QfBPRu1ClkokHeGDgAGCx
-If no kids with you, this place is a bit weird and quirky and something a bit different. Upstairs is a small bar/absinthe bar. Downstairs, is a quirky museum collection. https://thelasttuesdaysociety.org/ Nearest station is Cambridge heath overground.
-Another option is to walk to London Fields. There is a high St with shops and also London Fields park and Pub in the Park. Nearest overground- London Fields. Their market day is Saturday, so that is an option if not there on a Sunday.