During my first trip to London, I did not get a chance to get to some friendly "non-touristy" pubs. I will be on my own and traveling in November. I hope to be staying in kensington or bloomsbury
Many of London's pubs have been taken over by corporate entities (Taylor Walker, Youngs for example) and turned into gastro pubs. BUT keep hope alive, there are pubs that are frozen in time, not modernized and even some of the corporate owned places are without hordes of tourists.
I travel to London nearly every year and am always looking for "traditional boozers." Unaltered pubs that are watering holes for the locals. Between my nearly month long sojourns last year and in 2015 discovered some gems.
Near the wonderful Wilton's Music Hall and within walking distance of the Tower Bridge is the Princess of Prussia.
http://www.princessofprussia.co.uk Went in after seeing a Panto at the Wilton Music Hall. It was quiet . There's a back room with comfortable chairs to enjoy a good book and a pint.
Not in central London but easily accessible by tube is the huge Prince of Wales on Willesden. Was staying in an Airbnb flat in that area at Christmas and discovered the pub walking back from exploring Kilburn High Road. Actually thought it was closed as it was around 4pm on Christmas Eve, but no, it was open. For over an hour it was just me and the Santa Claus hat adorned bar maid. Slowly a couple of elderly gentlemen arrived and sat near the bar. Clearly regulars. I was sitting near the dart board where there was a comfortable couch and nearly floor to ceiling windows. By 6pm 5 people and time for me to return to the flat to cook dinner. This pub is a 15 minute walk from either Queen's Park or Kilburn tube stations.
Another place that totally surprised me was Kendrick's Bar on Harrow Road. A friend recommended it as a spot to meet up. From the outside (its purple) I expected a posh interior. Not the case. Was nearly the youngest person in there and I was born when Truman was in office. Pool table, stools at the bar, some upholstered booths, locals. LOVED it!
On a walk mostly along the Thames from Tower Bridge to Rotherhithe found myself enjoying a pint and lunch at the Angel, a Sam Smith pub. Lovely place. It was November so too chilly to sit on the patio but a really nice environment.
The Castle on corner of Holland Park and Clarendon Roads was the go to pub during the 2015 trip as I was staying in another Airbnb flat in the neighborhood. Pleasant atmosphere with a nice Xmas Tree and nary a tourist. Good food as well.
Last but not least and here you will find some tourists but you are there to see the art deco interior. The Blackfriar Pub right across from the all glass at Blackfriar station. Love the dichotomy of old London and new London.
Research beerintheevening and fancyapint. Good websites to locate pubs.
Walking distance from Bloomsbury there's The Old Mitre in Ely Place, The Ship on Little Turnstyle, The Seven Stars on Carey Street, then Sam Smith pubs The Princess Louise and Cittie of Yorke (great pubs, though Sam's beer is a bit ropey) and the shabby but cosy Lamb on Lamb's Conduit Street. Even in central London there are loads of great pubs.
Here's a recent thread with lots of info: https://community.ricksteves.com/travel-forum/england/mcpubs-in-london
An interesting choice relatively near Kensington is the Earl of Lonsdale at the corner of Portobello Road and Westbourne Grove, which has a full set of Victorian partitions between the individual tables to divide it up into small rooms.
We recently stayed in Kensington and enjoyed a nice dinner at The Stanhope Arms near Cromwell Rd and Gloucester Rd. It's a Taylor Walker pub but was filled with locals during a low-tourism period. We also enjoyed The Prince Edward - not sure how "non-touristy" we could say it is - the crowd was harder to read but it was a nice place with good food.
When in doubt, I seek out Fullers pubs as they normally have decent food and atmosphere, and I enjoy their various beers. The brewery is in London and they operate pubs throughout southern England. Near Kensington/Earl's Court, my standard go-to pubs are the Hereford Arms (near Gloucester Road tube) and the Blackbird (across the street from Earl's Court tube entrance). Both have a nice atmosphere, reasonable mix of friendly tourists and locals. Hereford Arms has a better menu and a separate dining area. Closer to Kensington High St is the Scarsdale Tavern (also a Fullers pub) which is a nice, cozy place too. It can be hard to find a pub without any tourists, but if you are staying nearby, these three are good options.
The Pembroke near Earl's Court/West Brompton is also a nice pub with good food (especially the Sunday roasts) http://www.thepembrokesw5.co.uk/
Finally, the Champion pub (between Notting Hill Gate and Queensway tube stations, near Hyde Park) has been suggested to me as a good lunch stop with more of a "locals" feel and interesting beer selection. I haven't been there but am passing on the suggestion!
I like The Victoria, between Paddington and Hyde Park. It's a Fullers house.
Here is a list from the Telegraph of London's most historical pubs that I have been saving for future visits.
I am hoping to get back to the Counting House Pub ( near St. Paul's Catherdral) this year when I am in London. That is a very nice pub too.
Blackfriar's has become the traditional "first evening" stop for my family when we're in London. The atmosphere can't be beat and has an intriguing history which any of the barkeeps will be happy to share with you. It's located on Queen Victoria St., near Blackfriars Bridge. We love the place.