Like most of London's museums now, the Science Museum in South Kensington charges for admission. But for those eager to broaden the frontiers of their knowledge, they can boldly go where few have gone before - to Willesden Green in the capital's north-west - and have an alternative science lecture for free.
Every week expert "alternative thinkers" give free talks. Last night's advocated the theory that diseases arrive on our planet on comets that have travelled from outer space.
While increasing parts of the capital's high-culture move to charging customers, with the new head of the Victoria and Albert an advocate of admission charges, there remains a bustling alternative culture for the visitor or family on a day out. And it's free. So too are the national monuments to high culture: the British Museum, the National and Tate galleries. Up to 50 lesser museums and galleries in London are still free.
But with the Science, Natural History, National Maritime and Imperial War museums all having compulsory charges, and the V&A asking euphemistically for voluntary donations, it can pay to think laterally. And some of London's free attractions certainly demand a certain amount of lateral thinking.
They still change the guard at Buckingham Palace. And it is still free, though you need a pocket calculator to plan your visit. It is advertised as being "on alternate days, on even dates in November and December, not in very wet weather or on certain ceremonial days".
Free too is the Albert Memorial Visitor Centre in Kensington Gardens. The memorial itself, a masterpiece of Gothic revival with nearly 200 statues, is shrouded by scaffolding and hidden from view, but an exhibition in the adjacent visitors' centre shows what it would look like if it were visible.
The London Tourist Board points out that the capital's parks are free, many with free concerts. So too is the capital's pageantry - events such as the State Opening of Parliament, the Lord Mayor's Show, Trafalgar Day Parade and Trooping the Colour - though it adds laterally "although sometimes you have to pay for the best view".
It is proud of what it calls free eccentrics' entertainment, such as Speakers' Corner and the Peter Pan Cup Swimming Race. There is non-eccentric entertainment in places like the South Bank Centre foyer, Westminster Abbey and Covent Garden piazza. The Oxford and Cambridge boat race can be viewed for free, so can the London marathon and the Notting Hill Carnival.
Free day in London
10am: British Museum.
11.30am: Watch the Changing Of The Guard, St James's Park.
2pm: National Gallery.
4pm: Visit the 10 Bears' Christmas Grotto at Harrods (Beware: the toilets cost pounds 1).
6pm: Join in with carols in Trafalgar Square.
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