Guided Tours

Look at London Walks.

https://www.walks.com/

St Paul’s:
https://www.walks.com/our-walks/secrets-and-spendours-of-st-pauls/

Westminster Abbey:
https://www.walks.com/our-walks/westminster-abbey-tour/

Tower of London:
https://www.walks.com/our-walks/the-tower-of-london-tour-1-1/

I take one of their walks each time I’m in London.

Most recent ( this summer) Inns of the Court.

Guides are excellent. Groups are small. Cost is practical and inexpensive for London

I recommend the Verger Tour at Westminster Abbey. Tower of London Beefeater tours are free, but the groups can be quite large.

I 2nd Carol's suggestion for the Verger tours of Westminster Abbey. The access to the Edward the Confessor chapel is restricted as the floor is not up to having lots of traffic (per the last verger with whom I toured, lol) but the Verger tours are taken in this beautiful small burial chapel.

Westminster Abbey also has their audio tour available free on an app. Download this before you go so that if you want more information about something you can go back after the Verger's tour and listen to the Audio guide.

I do enjoy London Walks, but I'd use the Verger tour for this venue.

Thanks everyone for your recommendations!