@mnd999 @DoomsdaysCW There are many Linux Cafes (or similar) in many places. I don't know about London specifically, but I would be very surprised if there isn't. You could try checking https://endof10.org.
EDIT: I am very surprised, it doesn't look like there is. You could always start one? We started off as me saying " You know what we should do? ..." to some friends at a social over drinks. It really is that simple.
"Want to start a Linux Repair CafĂ©? We have developed a starter pack to help you do just that (available in Dutch, English, French, German and Spanish). Existing Repair CafĂ©s in our network can easily download it via their Repair CafĂ© account. You can access it by clicking on the âDownloadsâ button. Let us know when youâre ready to open, so we can add your cafĂ© to the world map.
"If you do not yet run a Repair Café within our network, you can register and download the starter pack for a Linux Repair Café.
"All Linux Repair CafĂ©s are marked on the Repair CafĂ© International world map. This allows anyone interested to see which Repair CafĂ© can help them switch to Linux. You can see which Repair CafĂ©s have gone before you by typing âlinuxâ into the search field."
https://www.repaircafe.org/en/more-and-more-linux-repair-cafes-including-france/

Since the Linux Repair Café became available in five languages, the number of Repair Cafés offering Linux installation has grown rapidly. This is also the case in France. Volunteers from two French Repair Cafés share their experiences and offer advice.