Leave Brussels around 6:30–7:00 AM and follow the E40 toward Calais, allowing roughly 6–7 hours door to door, including the drive to Folkestone, Eurotunnel check-in, the 35-minute crossing, border formalities, and London traffic. Reserve a vehicle space on Eurotunnel Le Shuttle in advance and arrive at the terminal at least 60 minutes before departure; keep passports, travel documents, and any required UK entry authorization handy. Once in London, avoid driving into central areas where congestion and parking are expensive—leave the car at your hotel or a pre-booked car park and continue by Tube or taxi. A Thameslink train from the London Bridge area is also useful if your accommodation is elsewhere.
Head first to Borough Market in Southwark for a relaxed lunch and an easy first taste of London. Spend about 1½ hours browsing the stalls around Bedale Street and Green Market, with roughly £15–25 per person for a generous casual meal. The market is generally open Tuesday–Sunday, though individual traders vary, so check the official schedule before setting out; Saturday is the busiest day, while Sunday tends to be quieter. From there, walk west along the riverside to Tate Modern—about 10 minutes via Bankside—and allow 1½ hours for the Turbine Hall and permanent collection. General admission is free, but special exhibitions usually require a ticket; check closing time and reserve exhibitions online if one interests you.
Cross the Millennium Bridge toward the City for superb views back to Tate Modern and directly toward St Paul’s Cathedral; the crossing itself takes only about 10 minutes, but allow half an hour for photographs and the riverside outlook. Continue to St Paul’s Cathedral, where the nave, dome interior, and—if open and you still have the energy—the Whispering Gallery and Stone and Golden Galleries make a worthwhile visit. Paid sightseeing entry is typically around £25–30 for adults, with last admission usually well before closing, so check the date-specific hours and arrive with enough time. Finish by taking the Central line from St Paul’s to Holborn and walking to Seven Dials and Covent Garden—or use a taxi if everyone is tired—for a lively evening among pedestrian streets, performers, and shops. Allow about two hours for wandering and dinner; nearby restaurants commonly run £30–50 per person, and booking ahead is sensible, particularly around Covent Garden.