One small bottle of beer (1.6 units), or a glass of wine.
Three units, downed quickly, will put an average adult at or above the limit. Food slows absorption slightly, but the alcohol is still absorbed. There are many variables, but the body removes about one unit of alcohol per hour (one unit = 10ml = 8g). Accumulation is guaranteed if you drink more than one unit per hour. It is a linear process;
Over a two hour meal: Four bottles of Peroni = 6.4 units. Two units are removed so the body will contain about 4.4 units. This is 4.4*8 = 35.2g of alcohol. This dissolves into 0.55 L/kg or 38.5 litres. So the blood alcohol concentration will be about 35200/38.5 mg/L = 91 mg/100 ml. That is over the limit of 80 mg/100ml and it would be illegal to drive.
If you have a crash, backwards extrapolation is a valid legal exercise, which is why so much effort is placed on understanding the disposition of alcohol.