Standing in Grot Market, the central square of Brussels and the destination is the center of London, Eurostar is the best choice. Many will go to the airport. Eurostar is not only more exciting and comfortable, but you can reach central London at the same time as flying.
I am addicted to European trains. A typical trip includes meetings with German partners in Heidelberg, Munich and Stuttgart, followed by a stop at a European headquarters in Brussels. After arriving in Frankfurt, I chose trains instead of cars and planes. They are fast, punctual, comfortable and take me to business centers in the city. My train arrives on time, regardless of the weather and without stress after hours of travel or airport navigation.
Eurostar provides all these benefits and more. It is a five-minute walk from Brussels Square to the Midi / Zuid train station. Eurostar travels to London ten times a day. The minimum waiting time is a comfortable living room. Journey to St. Pancras in London lasts 2.5 hours. Plenty of legroom, Wi-Fi, cell phone availability, catering services and other amenities come from driving. From St. Pancras take a taxi or a short metro train to reach your destination. For me it was two stops to Baker Street. Counting the hour at a station in Brussels and a taxi in London / subway time, total travel time is about 4 hours.
A leaflet from Brussels Square takes 45 minutes by taxi to the airport. Security and waiting is 90 minutes. The flight takes 75 minutes. Heathrow airport is located quite far from central London. The taxi is 40 minutes outside of peak hours. Heathrow Express will lead you to London in 25 minutes. Assuming only 15 minutes to get around the airport, Heathrow Express and 15 minutes more to your destination in London, total travel time is about 4 hours.
When you go to your London hotel or meet which travel option is more convenient and relaxing? What gave you more time to prepare a presentation or talk to the office? Which option is the most exciting, for example tunneling under the English Channel at 186 miles per hour? Eurostar!
I admit that I am addicted to European trains. Next time you want to get to London in Belgium, Germany or other places on the continent, try Eurostar.