GUTTED - Blackleg !!!!

I planted several different types of seed potatoes including 'Desiree', I noticed some yellowing leaves in the rows of Desiree yesterday and on closer inspection today have discovered that it's blackleg. 

I have four rows of about 12 Desiree, the neighbouring potatoes on either side (Golden Wonder & Romano) are unaffected so far and it just seems to be just the Desiree that have it, all the potatoes apart from one type (Saxon) came from the same supplier, the others potatoes types being grown are Pentland Javelin, Blue Kestrel and Estima.

So far I have dug up and removed the obviously affected plants (yellow leaves, black mushy and watery stems), some of the other plants also had some discoloured leaves but the stems seem fine so I have left them for now pending further advice although I think them being OK is just wishful thinking on my part.

Having not come across this before my questions are (sorry but there are a few) .. .. ..

1. Should I remove all the Desiree, just the ones showing obvious signs of disease or all that I suspect might be affected?

2. How fast will it spread to the other rows?

3. Will the disease stay in the soil, if so how long will it be before I can plant in the same area again?

4. Why is it only the Desiree affected - did I get supplied with a bad batch?

5. Can I eat the potatoes that I dig up when removing the plants.

6. Is it worth keeping the plants in the ground for as long as possible or will this just spread the disease?

Oh dear 

http://www.rhs.org.uk/advice/profile?pid=223

1. Remove the affected plants pronto and I'd just keep an eye on the others.

2. It's mainly weather dependent, so spread partly depends on how closely you've spaced the plants and how the weather dries up / becomes less humid.

3. Rotation in the usual way should be fine.

4. It may have been a poor batch, but it may also be that they are a less resistant variety.  (Have a look on the potato database for info on resistance - I haven't done so).

5.  If they look OK, I'd eat them pronto.  Don't try to store them.

6. Remove any infected plants pronto.

See the RHS guide above for more info.

Will I be able to contain this disease? I am worried that I am going to loose the whole potato crop.