The process of buying a house in France is certainly not something that can be done in a rush. And especially if you have bought a house with the intention of settling there permanently, you will have a lot of things to sort out for your emigration. Emigrating requires more organising than if you were moving within the UK. Think not only of the longer distances over which you are moving your belongings, but also of other practical matters. Some examples of this include the timely cancellation of subscriptions to magazines and newspapers, but also your television and internet contracts and your gas, water and electricity accounts. Quite often, there is a minimum notice period associated with these contracts that you are expected to take into consideration. Your regular mail must be rerouted over time, and to be sure that nothing goes missing, arrange for any remaining post to be forwarded to your new address abroad.
The emigration rules for Europeans within Europe are flexible, but be aware that there is still a lot of paperwork to sort out. Naturally you will need to deregister yourself from your local community, and register yourself in your new community. Furthermore, you may wish to take your British car with you to France. If you are a pensioner, or you plan to retire soon, do also notify your pension provider that you are emigrating so that you do not run the risk of losing your pension funds.
For your emigration it is handy to keep an emigration checklist with you, to maintain a good overview and to avoid forgetting things. That way, you will know for sure that you can depart for France without any concerns!