Hi Steven,
you might have already taken your trip (if so hope you had a great time!).
Anyway, I have not used the BMI lounge in international departures but I think it is pretty similar to the one in domestic departures at LHR - which I have used many times.
I agree with Michael's comments - very limited food and all self service. They have a couple of TV's, the usual array of newspapers and a few magazines. The domestic departure lounge is quite large and its never too busy. Two different kinds of Red and White wine, 3 or 4 beers and basic Gin, Vodka and Whisky. Bottled water and soft drinks in a fridge and couple coffee machines.
Most of the BMI lounges are actually 2 lounges in 1. This is not at all obvious. There is a sign which says BMI business lounge AND the BMI Diamond Club lounge. The Diamond club lounge is actually upstairs from the normal business lounge at domestic LHR. Its not a lot different but has few more drink choices and things like cheese and biscuits - also quieter and less busy. There is also a small bar in addition to self service but no-one ever been on duty at the bar when I've been! You need a star alliance gold or above to get in - no AMEX or Virgin Gold will get you entrance.
In general I have always found BMI service to be pretty good on the flights - mind you only ever been on 1 or 2 hour flights.
cheers
Jock