The French do have excise duty on wine, it’s just not very much - about 3p a litre compared to our nearly £3. They do however charge VAT at 20% as we do.
In my experience, though, what makes the difference in wine prices is the buying power of the supermarkets. French supermarkets do have wine at £3-£4 a bottle, but not much, and you wouldn’t want to drink it. However they have plenty of lower mid range wine for £5-£8 which you would be paying more than double for over here. At the top end, prices are comparable. Conversely, non-French wine is typically cheaper in U.K. supermarkets than France, principally because the French sell so little of it they don’t have