Early morning in Trafalgar Square
After a night of wining, dining or partying, grab a taxi — well, OK, a night bus — and take a small hours' stroll around Lutyens' Grade-II listed fountains, by now pale green water mirrors unruffled by tourists, drunks or the banished pigeons. Time it right (about 8.25am) and you will hear a hiss and a splutter as the fountains spring to life. Nearest station: Charing Cross, Embankment.
Keats' House, Hampstead
This is the house where John lived, a white Regency villa in one of the prettiest parts of London, where the young poet fell in love with the girl next door before dying tragically in Rome. The story has just been told in Jane Campion's new film Bright Star and the house has just been beautifully restored, thanks to the Heritage Lottery Fund and a loyal band of volunteers. Open Winter Friday to Sunday 1pm-5pm, Summer Tuesday to Friday 1-5pm; £5 adults, £3 concs keatshouse.cityoflondon.gov.uk.
Lunch and a matinee at British Film Institute, Southbank
There's something about the revamped BFI auditorium that makes it feel intimate and studenty all at the same time. Skive off work to eat at Benugo's Riverfront Cafe, which buzzes with artsy conversation, before disappearing into the darkness to watch Breakfast at Tiffanys or Casablanca (Valentine's offerings), or see the sparks fly in February's Hepburn and Tracy season. When you come out, the night will still be young… Weekday matinees £6.40 for non-members (£5 on Tuesdays, £9 at weekends) from bfi.org.uk.
Rooftop dinner at the Boundary, Shoreditch
Conran's charming hotel in an old printworks in Shoreditch has a rooftop terrace kitted out for winter with heaters, cosy Welsh blankets, warming foreign alcohol and a Twitter feed to tell you if it's open or not in London's newly extreme climate. In summer, you can just kick back, enjoy Champagne and oysters or steaks from the barbie, and toast each other's health as the sun sinks over the warehouses and City towers to the west. Opening hours are weather dependent - check the Twitter feed in winter. theboundary.co.uk.
Isabella Plantation, Richmond Park
If ever there was a gorgeous walk in London, this is it. The name is not as romantic as it sounds — it may well be a corruption of the word for dingy, boggy ground — but who cares, when you can stroll among camellias, magnolias, daffodils and bluebells in the Spring, closely followed by rhododendrons and azaleas. In winter there's a heather garden, perfect in the snow. Nearest gates: Ladderstile or Ham, see royalparks.org.uk.
Look for love letters in Heywood Hill, Mayfair
There is nothing more romantic than browsing in a bookshop with somebody special. If that means anything to you, this is the one to choose: Heywood Hill has been squeezed into this Mayfair terrace for over 70 years (Nancy Mitford famously minded the shop while its owner was at war) and they do a great line in collected letters between friends and lovers. 10 Curzon Street, W1; www.heywoodhill.com.
Window shopping at Clarendon Cross, Notting Hill
Even non-shoppers can't fail to enjoy a potter around the chi-chi-ness of this well-heeled crossroads in Notting Hill. Virginia's really does stock romantic lingerie, rather than the high-street-porn variety, there are homeware shops and a bit of everything gorgeous at The Cross. Then you can go and curl up on an old pew at Julie's and while away a wine bar afternoon. Nearest station: Holland Park tube. clarendoncross.net.
Sir John Soane's Museum by candlelight
On the first Tuesday of each month, from 6-9pm, this extraordinary house on Lincoln's Inn Fields is lit only by candles. See the Egyptian antiquities, Oriental objets, neo-Classical sculptures, furniture, stained glass and intricate timepieces as the great architect and collector himself would have seen them. Nearest station: Holborn soane.org. Last entry 8.30pm. Free.
Galvin at Windows, the Hilton
There's something weirdly un-London about the restaurant on 28th floor of the Hilton on Park Lane; it's more like being in Hong Kong or Sydney, until suddenly the lights far below resolve themselves into a circle (the London Eye), a triangle (the top of Canary Wharf) and other oddly familiar shapes. Chris Galvin has just got his first Michelin star, so it's not going to be cheap as chips. But romantic? Oh yes. Nearest station: Hyde Park Corner galvinatwindows.com.
Sunset on Waterloo Bridge
Yes, yes, it's a cliché, but the plainest of London's river crossings has its own song (Waterloo Sunset by the Kinks), its own movie (Waterloo Bridge, starring Vivien Leigh) and the best views of any bridge in town. As the sun goes down, the city lights up; from the Eye and the National Theatre to the Savoy and Charing Cross Station. A good sunset will finish you off completely. As Wendy Cope's proem goes:
'On Waterloo Bridge, where we said our goodbyes,
The weather conditions brought tears to my eyes.
I wipe them away with a black woolly glove,
And try not to notice I've fallen in love.'
Nearest station: Waterloo or Embankment Tube.