The first challenge you will have to face is of course the traffic. As I wrote earlier the direction of the travel is a real challenge for continental europeans. 
Next is the chaotic traffic situation in general, especially for people who are from rural areas. A lot of people get headaches when going by tube and breathing is a problem too because of the dust and the used air. But the greatest challenge you will encounter is using the English language in all situations and understanding the different accents of the people of London.
Next is the chaotic traffic situation in general, especially for people who are from rural areas. A lot of people get headaches when going by tube and breathing is a problem too because of the dust and the used air. But the greatest challenge you will encounter is using the English language in all situations and understanding the different accents of the people of London.