You would need around €1,491.60 (£1,263.72) in United Kingdom to maintain the same standard of life that you can have with €1,420.58 in France (assuming you rent a place to live in both cities). This assumes net earnings (after income tax).
If you eat out 4x a week in an inexpensive, and 1x a week in a mid-range restaurant you will pay €28.68 more in United Kingdom (€174.68) than in France (€146.00).
For monthly supply of groceries worth €236.76 in France you will pay €35.51 less in United Kingdom (€201.25). If you are an average smoker (1 pack per day), you'll spend €108.68 more on cigarettes each month than in France.
While using public transportation in United Kingdom using the monthly pass you'll end up paying €8.91 more than in France. However, if you will be driving a car 32 km on average each work-day, each month you'll spend €1.86 more on gasoline than in France.
To buy an 85m2 apartment in United Kingdom city centre you will need €365,077.53 which is €48,861.42 less than in France (€413,938.95), however to buy one outside of the city centre you will need €269,455.70 which is €10,307.70 more than in France (€259,148.00).