“Do not add UK cables, switches and sockets”
There are fundamental differences between French and UK electrical systems and UK cables, switches and sockets MUST never be applied to a French house. They are just not compliant.
Admittedly the cost of purchasing electrical items is much more expensive than in the UK. We certainly noticed the price difference when we moved to France, but it is what it is. You can be forgiven for thinking that purchasing UK items is cheaper in the short term but long term could have devastating consequences.
Be mindful that if there is a fire caused by an electrical fault linked backed to non compliant work, you are compromising your insurance.
Be mindful that when you sell your property, it will be subject to an electrical diagnostic report and will include the identification of abnormalities such as the use of non compliant products.