Book for Christmas at Kew Gardens now.
One night Meander about Winter Wonderland in Hyde Park;
Online check the following venues websites for music options:
Cadegon Hall ( classical music ) Ronnie Scotts for Jazz, Wilton’s Music Hall.
Various churches will have Christmas Concerts. Walk inside any church you pass and look for flyers mentioning a performance.
You’ll find plenty of interesting booths at Spitalfields market. Bought Xmas cards and ornaments there more than once.
Also look in the entry areas of churches and cathedrals. Many have boxes of Christmas cards with sales benefiting local organizations.
As far as markets; Portobello Rd, Brick Lane, Covent Garden, Southbank, Leicester Square. Carnaby Street is colorful.
Churchill War Rooms are great. So popular now you need to book tix in advance.
For restaurants: Dishoom, Nando’s, Wahacas, Wagamama, Bills, Leon and Five Guys chains.
One of the best meals I’ve had in numerous London trips was at the Dragon Inn in the Richmond. They serve Dinner only. Believe reservations a must.
I’m a fan of pub grub especially their soups and stews. Still dream of the pumpkin and sage soup I enjoyed at The Dove in Hammersmith.
Try to get a reservation at Putney Pies.
If you like walking and if weather is good take a meander in Richmond Park to see the fallow deer. Then stop in the White Cross Pub for lunch. The Richmond neighborhood was untouristy before the popularity of the Apple TV series Ted Lasso. Now, not so much. Still its an interesting London neighborhood to explore.
EDIT: check to see of the Eel Pie Island artisans are having a Christmas open house.