In article , Genie
writes

The "grassed" area consists of nettles and dandelions, with thin
straggled bits of grass at the edges. The area is shaded by the corner
of the house in the morning, and gets full sun from about 3pm onwards,
so the ground is normally wet underfoot until that point. The area
under the kitchen window gets full sun all day.

I spent a couple of hours last week trying to dig up some of the
nettles at the edge of the "grassed" area to see if it was possible to
remove them without sacrificing what little grass remains. However, I
discovered that there is a web of inch thick nettle roots about 20cm
below the soil surface, and that if I tried pulling them up, the
result looks like the surface of the moon. Am I right in concluding
it's better to redo the lawn from scratch?

Possibly. Alternatively, you might find that repeatedly closely mowing
the lawn will get rid of the nettles in time - they'll put energy into
making new leaves, which you'll then mow off, and eventually they'll run
out of energy.

I consulted with our landlord, who is willing to run his rotorvator
(what is this?) over our "grassed" area,

an engine driven thing with sharp blades which cuts everything up into
bits and turns the soil over.

which he says will let us
seed the lawn again. However, I'm dubious as to whether this will get
rid of the nettles or just distribute their roots more widely round
the garden and let them take over even more space.

You're right to be dubious. It won't distribute the nettles beyond the
rotivated area, but it will leave bits of root to reappear as nettles in
your grass. You won't be able to mow the reseeded area until the grass
is big and tough enough, so the nettles will get a head start.

I'm interested in
gardening, but my skill and experience are close to zero.

We all started that way! :-)
Carry on as you are doing - observing and thinking - and you'll soon be
surprised at how much you know.


--
Kay Easton

Edward's earthworm page:
http://www.scarboro.demon.co.uk/edward/index.htm