Tickets went on sale this morning for the annual New Year's sale on selected London theatre performances during January and February. This sale is run by the Society of London Theatre (SOLT) a not-for-profit organisation representing the theatre industry. SOLT also runs the Olivier Awards and the TKTS booth in Leicester Square.
To get the sale prices, make sure to book within the New Year's Sale page: https://officiallondontheatre.com/new-year-sale/
I'm seeing Company with Patti Lupone in January at the Gielgud Theatre, a £49.50 ticket for £30.