I live in Surrey ( part of Greater London) which is approx 30 miles from my in laws house in London City. It takes me minimum of 1.5 hours to reach their house on car. I visit them with my wife for at least couple of times a month and most of the time stay over for a night due to long distance travel.
As you mentioned that your house is in greater London and your in laws are living in London city in another word your place is part of that metropolitan city then your namaz is full distance and time of travel will not make it qasr.