I'm not championing price competition above all, I am saying that below cost selling is actually irrelevant to price competition, if you are talking about independent off licences trying to compete with supermarkets on the price of canned beer.
We have two different business models here.
1. The independent off licence has to make a profit on the beer they sell.
2. The supermarkets are willing to make a loss on the beer they sell in order to get you in to buy other products.
1 cannot, under any circumstances, compete with 2 on price.
If you ban promotions they will simply have a regular price that is as cheap as the promotional price would have been. Effectively they run the promotions for longer and don't call them "Special Offers".
If you ban below cost selling the supermarkets will simply sell at cost price. This is still cheaper than the cost + profit the independents must charge.
This is not a battle the independent retailers can win and perpetuating the myth that cheap beer is causing problems in this country is only giving ammunition to the neo-temperance brigade.
Also, as most alcohol legislation tends to be pretty ham fisted, there would likely be unintended consequences. For instance, a ban on below cost selling would make your local publican handing a free pint to a regular illegal.
So the supermarkets keep doing what they do, the independents are no better off and the consumer is a little worse off. Great.