Malc,
They should have some sort of number on them , whip one out and have a look. However, under no circumstances give the car ANY full throttle acceleration until you have checked this, as you could melt the plugs / engine .

The standard Ford Escort Cosworth plugs are NOT suitable for this power level if this is what they have put in. Get them to swap them for the Motorcraft AGP071s, they are a lot cheaper as well and can cope with sustained 2 bar of boost no probs (I run these in my own car). They will probably try and tell you they are not suitable, but the ones they have put in won't take the heat level of your conversion, whereas the 071s will.