Quote from HMRC:
"Although there are no limits on the amount of alcohol and tobacco you can bring in from EU countries, customs officials are more likely to ask you questions if you have more than:
• 3,200 cigarettes
• 200 cigars
• 400 cigarillos
• 3kg of tobacco
• 110 litres of beer
• 90 litres of wine
• 10 litres of spirits
• 20 litres of fortified wine (for example port or sherry)"
Essentially, there is no limit but they will be suspicious of any amounts over this. Typical things they look for include concealment (including a casually draped jacket), multiple brands, source of income, inconsistencies in answers (such as how much you smoke). You cannot sell (even at cost) anything you bring in. If Customs think it is for commercial purposes, they can seize your vehicle and whilst you have the right of appeal, it all becomes a major pain in the neck