You would need around €1,266.52 (£1,127.09) in United Kingdom to maintain the same standard of life that you can have with €1,266.52 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 €9.53 more in United Kingdom (€82.03) than in France (€72.50).
For monthly supply of groceries worth €211.08 in France you will pay €40.10 less in United Kingdom (€170.98). If you are an average smoker (1 pack per day), you'll spend €93.39 more on cigarettes each month than in France.
While using public transportation in United Kingdom using the monthly pass you'll end up paying €5.52 more than in France. However, if you will be driving a car 32 km on average each work-day, each month you'll spend €1.30 less on gasoline than in France.
To buy an 85m2 apartment in United Kingdom city centre you will need €347,564.82 which is €66,374.13 less than in France (€413,938.95), however to buy one outside of the city centre you will need €256,529.96 which is €2,618.04 less than in France (€259,148.00).