Rick Hughes wrote:
I bought in 30 tonne of top soil last year, and noticed the mini hill, has
now sprouted a thick layer of Horsetail.
What is the best way to kill this ... I will not be growing anything on this
soil for at least another 2 years .. so can afford to use something strong
on the stuff.

Thick, strong, expensive, durable, heavy, dark ground cover material.
Cover the lot for two years and then dig out the dead weed )

A quick Google around suggests that a Glyphospahte (Roundup or Tumble weed)
or Dichlobenil (Casoron G) product should work ?
Anybody any experience of how good these are on Horsetail ?

No. Nothing kills horsetail but digging them out.

On the Glyphospahate solution, a couple of posts mention 'Glyphosphate
Professional' is there much difference, or is this just a different
dilution ?

The same - you will notice as the years go by how many products change
their name so that it appeal once more to the people who are naive
enough to beleive that the chemicals used for generations has suddenly
another ingredient which will totally for ever kill all weeds and
pests. Sadly it's not the case and it carries on the production of
those poisons, fatten wallets and destroy many gardens in the process.