I found Ann Dix's article, 'Concrete issues' (cover feature, 30 July) very good stuff - concise, interesting and fair.

I went up to see Northwick Park the other day (as its architect, I visit it from time to time) and was enchanted to see that it is in the process of absorbing St Mark's Hospital, and that it seems to have done so with entirely appropriate means - indeed with brilliance.

A corridor and lift system have been clamped to the existing buildings, giving a new access point from the centre of the old Medical Research Council blocks. I think it is brilliant (who did it, I wonder?) because it takes the idea of the street, which is the big notion at Northwick Park, and adds another one - vertical as well as horizontal - just as if it were a real village. It shows how a hospital can roll with a developing future if it is set up to do so.

It's funny how Northwick Park now looks better than it has ever done. Probably the growth of the landscape has a lot to do with it, but the concrete also looks better than it did. There is now so much staining and lichen growing on it that it seems rather mature, like old stone. Or is that just the eye of love?

The evidence of growth and change is another life-giving development.

John Weeks

London N6