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If your visa is a single entry visa, you must replace it before you return to France. Normally you would replace it with a carte de séjour (residence permit) before you leave France. If the number of entries is otherwise limited, then the answer depends on how many times you have already used the visa to enter the Schengen area.
If the visa is issued for multiple entries, then you may leave and reenter France as many times as you like during its period of validity.
The question of whether you need a UK visa is separate. You cannot use your French visa to enter the UK. You may need to apply for a UK visa, depending on your nationality.