Transit visa to the UK is necessary. The consulate recommends that you open a transit visa before traveling. Consider it as much time as an ordinary visa, because the documents must be submitted in advance, and not the day before. There are also frequent cases when a transit visa is opened directly at a British airport. But the official services can not guarantee the absence of problems on the border, which, unfortunately, are fraught with deportation back to Russia.

The distance between the airports of Gatwick and Heathrow is about 45 miles (just over 70 km), the transfer time takes about an hour taking into account possible traffic jams.