You would need around €1,231.99 (£1,084.47) in United Kingdom to maintain the same standard of life that you can have with €1,219.80 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 €10.42 more in United Kingdom (€82.92) than in France (€72.50).
For monthly supply of groceries worth €203.30 in France you will pay €36.59 less in United Kingdom (€166.71). If you are an average smoker (1 pack per day), you'll spend €96.72 more on cigarettes each month than in France.
To buy an 85m2 apartment in United Kingdom city centre you will need €351,376.82 which is €62,562.13 less than in France (€413,938.95), however to buy one outside of the city centre you will need €259,343.51 which is €195.51 more than in France (€259,148.00).