No it isn't, at least in UK in 2010.
It's the best data I could find and it will require some calculations. I will try to err in favor of the claim in order to disprove it convincingly.
According to the General Lifestyle Survey Overview and in particular the General Lifestyle Survey - Drinking tables 2010 (Excel sheet 609Kb) found here, in particular Table 2.16.1
The Units and unit% columns are mine and are so calculated:
- using the Rural units
- assuming 0 units for nothing, 2.5 units for up to 4/3, 6 units for up to 8/6, 10 units for up to 12/9, and 15 units for more than 12/9. I believe I've exceeded in favor of the claim.
As you can see, the top 20% (more or less) consumes about 50% of the alchool (more or less). It's very far away from 80%.
Furthermore, there is no guarantee that the top 20% is the same people every week: if enough people have a sporadic wild night out once a year, they would appear as heavy drinkers in this table. This makes it either realistic or an over estimation in favor of the claim.
Based on this I can conclude that the evidence points against the claim.
1The double numbers "4/3", "8/6", etc. refer to male vs. female numbers of units.