Yes, plans start at £22.99 a year so it really makes sense to get a yearly plan - having to pay monthly would most likely mean eUKhost would have more admin and costs which would in turn mean the prices of the plans would go up.
Also, I might be wrong, but if you cancel the service after so long don't you get a refund of the complete unused months? Again, you will have to wait for confirmation off eUKhost for this
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