You would need around €1,426.16 (£1,237.86) in United Kingdom to maintain the same standard of life that you can have with €1,384.63 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 €24.51 more in United Kingdom (€170.51) than in France (€146.00).
For monthly supply of groceries worth €230.77 in France you will pay €39.23 less in United Kingdom (€191.54). If you are an average smoker (1 pack per day), you'll spend €101.07 more on cigarettes each month than in France.
While using public transportation in United Kingdom using the monthly pass you'll end up paying €7.22 more than in France. However, if you will be driving a car 32 km on average each work-day, each month you'll spend €0.28 more on gasoline than in France.
To buy an 85m2 apartment in United Kingdom city centre you will need €356,354.17 which is €57,584.78 less than in France (€413,938.95), however to buy one outside of the city centre you will need €263,017.18 which is €3,869.18 more than in France (€259,148.00).