I've done that, it's actually pretty fun and quick (about 2-3 hours). You take the train from Waterloo station and it takes you to Gare du Nord. I didn't really enjoy France that much, but you and your wife could have a different experience and really enjoy it. It also depends on how long you and your wife are planning on staying in Europe after your business trip. There are a lot of things to do just around London that time might be hard-pressed.
I suggest visiting Oxford if your wife decides to join you, especially during this time of the year. It's a medieval college town on steroids. Beautiful scenery, eccentrics everywhere, great architecture, pretty girls, lots of shopping, and tons of history. It's worth a day trip, just make sure you don't take a guided tour where you'll constantly be rushed and some old hag won't shut up on the overhead speaker. I think everyone else has covered the stuff to do in London. I recommend the outdoor stuff and taking in the atmosphere of places like Lygon st, Oxford St, Piccadilly circus, trafalgar square etc. over museums... because inanimate objects in air conditioned rooms won't be going anywhere.
This. And Stratford Upon Avon. And Stonehenge. Take a King Arthur tour. Hit up Paris if you want, but in my opinion, most people try to cram way too much into one trip ("Oh my, I have two weeks....let's see London and Paris and might as well fly to Amsterdam because it's only like an hour flight, if that, and might as well try to cram Berlin in as well...."). Point being, SEE London. It's truly an ancient city. A Roman city, in fact. Founded in AD 43 or something ridiculous like that. There is more to do and see and experience there than you can possibly imagine. If you see everything there that you want to see, head to Wales or Scotland for a few days, but in my opinion, save other trips for another trip! Just my experience and two cents.
