The main issue was the booze. One bottle of beer does not equal a party and I appreciate that the menu price of the prize was £300 but the cost price was not £300 which is actually what you would be spending. You probably did not even have to add any extra staff on a normal Thursday night so how much did the prize actually cost PLY?
If the prize was £300 cost price then we would have had a proper party!
I have run competitions myself through the business I run at the moment and from a retail / food establishment so I totally know the kinds of costs involved in it. I also know how to word an competition entry that does not mislead the winners of the competition so no one is disappointed with the outcome.