Hi, it is decided on a case by case basis - basically a judge has to consider the two together to determine that, but there is general guidance (albeit really, little more than logic) here: http://www.ipo.gov.uk/types/tm/t-other/t-infringe.htm. As you can see from his language in his email, the person who wrote to you has clearly read this or something similar.

The Nice Classification governs the breadth of a trademark. Basically you can't register two marks with the same name in the same major class for the same geographic area - that's a slight simplification, but serves here.

If there's (expected to be) confusion then one mark damages the other.

Also, it is worth firing of a quick email to ask if they have registered anything, and specifically, what they have registered. I wouldn't enter into any other correspondence until that information were given.

They have listed the 2 trademarks in letter 1. I guess thats what you are asking for advice about?

So they have, I only skimmed it. My bad.