Upvote:1
You are travelling from Schengen and returning to Schengen (i.e., not a bona fide transit case) and you will need a Standard Visitor Visa even if your visit is to attend a single event.
To apply both you and your wife should open an account at Visa4UK and complete the application. You will be able to apply at any British post that issues visas, so you could apply from within Schengen. However, the application needs to have lots of evidence submitted with it, so you may find yourself in a better position to apply from home.
You do not need to submit travel reservations or London hotel bookings with your application.
Adding... If you need a recommendation for an ethical and trustworthy adviser to handle your application, you can ask another question.