I would guess most of the country have had the right conditions at various times during the year for blight to thrive.
I get alerts from a website called blightwatch.co.uk via e-mail. You probably already know this but it's a service supported by the Potato Council. Traditionally the risk of blight is based on the calculation of Smith Periods. This service calculates the risk of blight down to post codes based on weather conditions and humidity. A Smith period is 3 days of the right conditions for blight to appear. 1 day is amber alert, 3, red alert. If you register on the site you can gain an insight going back several years as to the number of alert's in your area by post code.
My post code for instance has had very few Smith periods for several years and only the occassional blight alert in any given month This year alerts started in April and reached a peak in July with 15, which believe me is a huge increase in any previous year and the Smith period extended at one point to 5 days with only a gap of 1 day before another Smith period.
Check the site out and see what you think. Knowing when conditions are ripe for blight to thrive is like having an early warning system, I acknowledge you grow organic and can't advise on a product you could use to protect your crop as I try to grow organic small scale in the garden and would cover my spuds during blight alert periods if they extended beyond 2 days.