You would need around €1,272.99 (£1,142.35) in United Kingdom to maintain the same standard of life that you can have with €1,285.84 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 €8.84 more in United Kingdom (€81.34) than in France (€72.50).
For monthly supply of groceries worth €214.30 in France you will pay €42.86 less in United Kingdom (€171.44). If you are an average smoker (1 pack per day), you'll spend €90.87 more on cigarettes each month than in France.
While using public transportation in United Kingdom using the monthly pass you'll end up paying €4.96 more than in France. However, if you will be driving a car 32 km on average each work-day, each month you'll spend €1.82 less on gasoline than in France.
To buy an 85m2 apartment in United Kingdom city centre you will need €344,674.51 which is €69,264.44 less than in France (€413,938.95), however to buy one outside of the city centre you will need €254,396.68 which is €4,751.32 less than in France (€259,148.00).