Romance doesn't have to cost the earth, that's why many of the romantic things to do in London are actually free, so that you can be as spontaneous, fun and loving as you want. Walks in Hampstead Heath, or a free picnic listening to music floating across the hill, and capped off with a beautiful firework display could be the perfect romantic evening in the summer. If you happen to visit London in the winter, then you can still enjoy the many parks and gardens, perhaps in the warm tropical glass houses in Kew Gardens, or inside eating at Petersham Nurseries, just up the river in Richmond.
Flying high above London on the London Eye while holding hands and ooohing and aahing at the enormity of this mega city could also be considered romantic. Surprisingly, London Zoo can also be very romantic. Particularly around February and Valentine's day, the zoo likes to advertise its loving couples and babies born, and watching comical chimpanzees or the love of a penguin for its fluffy baby can inspire warm loving feelings in almost anyone.
Books are often a romantic escape for many people, so the Charles Dickens Museum or various literary walks around Bloomsbury might be the perfect romantic day for a bookish couple. If you are not a Dickens fan, then head over to the British library for great informative exhibitions and lots more books to choose from. At least one of these will rekindle that loving feeling.