Halloumi ended up too soft I made halloumi at the weekend using this process with cows milk. The rennet I used had a best before June 2014 date on it.

The cheese came out fine and tastes good after being brined.

However when I fry the slices of halloumi the result is that the cheese is too soft (by general concensus in my house) and doesn't 'squeak' like a true halloumi should.

So my question is what might be the cause for my too soft halloumi? and what can I do to make it firmer next time?

My initial thoughts are that I could 'press' the curds more before poaching, or it could be the rennet (although they seemed to work fine). Or it could be the cows milk rather than ewes milk.

It may also be that it will firm up whilst it sits in the brine. Does anyone know if this is the case?

Any thoughts?
You are right that you need to use pressure to get enough whey out of the curd to get a firmer cheese like halloumi.

I am surprised that the recipe you're linking to tells only to drain the curd in a sieve or cloth. Just draining the curd will give you a very loose or moist product similar to cottage cheese or quark.