Many pet owners in London are concerned about marauding packs of foxes attacking their pets. Foxes are protected in London and with no natural predator they have now reached hefty numbers in London.
It is our experience that foxes , generally speaking, will not attack domestic pets for food. There are too many other 'easy' sources of food in the Capital (rubbish bins , etc). There are some repellents that you can put in your garden to discourage them - make a note where they enter and leave your garden and use the repellents there - foxes always follow their previous trails.