I'm sure you will take the Eurostar to go to London, so...

If you are lucky, in France you will find someone with a car, like your mother, your father or, why not, if you are lucky, your Girl-friend, to drive you to the train station (Gare du Nord)... but be careful, when you arrive in London, you are alone and you will have to take the underground... with all your luggage! So try to get the smallest luggage as possible.

When I arrived in Waterloo, I had to fetch the keys of my flat in Marble Arch. So I had to take the Jubilee Line and then the Central Line. But due to technical problems, the Jubilee Line stopped when I arrived on the platform and I had to walk a long time with my entire luggage to the Bakerloo Line. So remember that walking with two suitcases and with a big rucksack is exhausting.

:: London Underground.

The price of transport is very expensive in London. It depends where you live in London and where is your work. But if you know that you will take the Tube at least three times one day, buy a day ticket and if you know that you will take the Underground during an entire week, buy a week ticket. Moreover, there is also a month pass (in magnetic form), an identity photo will be required.

For exemple :
If you buy a "Zones 1 & 2" ticket before 9:30am (Peak hours) you will paid £5.30 and after 9:30pm (Off Peak hours) only £4.30. So if you can take the tube after 9:30 it's better... for your wallet. Of course it is cheaper when you buy week or month travel cards.

In Zone 1, a bus ticket costs only 1£ and a day ticket costs 2£. So I recommend you to buy a day ticket when you know that you will do at least two travels a day.

If you have a tube day travel card no problem you can take buses without paying anything else all over the day. But the contrary is not possible: you can't take the tube whith your bus pass. Be careful, now in Central London you have to pre-purchase tickets, and you cannot pay on board.

If you buy a day ticket only once a week (to go to UCL for example) take advantage of this and in the evening take a bus to go in London center or to go to your best-friend house.