Looking at the
Evans site I'm assuming it's the non-disc Sirrus Elite, then it's a bit of swings and roundabouts. The Sirrus has a carbon fork while the Boardman Comp (again, assuming this is the version you're on about as it's £500) has Alloy, so Sirrus should be more comfortable over bumpy roads and stuff. Sirrus also has 3 chainrings at the front whereas Boardman has 2, so Sirrus has more gears, whether you need them or not is another matter. If my learning about gearing is working, the Sirrus has some lower gears for the hills but the Boardman will go a little higher for the faster bits
The Boardman has disc brakes though, which can be nice. Some people don't think there's a point to them on certain types of bikes (i.e. those who stay on the road) but should have better braking in the wet. The type of disc brakes on the Boardman seem to be ok, if not great, judging by what I've read of other peoples opinions. I've just got a road bike with disc brakes, been fiddling with them to get them setup ok, but I like them.
I don't know enough about the rest to even comment, but I'd go for a carbon fork if possible.
Boardman bikes have a good rep round here,
Halfords service can be variable. I certainly wouldn't say that Boardman was loads better than that Specialized, I'd go for the Sirrus but you might feel differently sitting on them both.