NVI (non-value indicator) stamps remain available for the designated service irrespective of price changes. 'E' stamps (which were only issued from 1998 to 2004) were valid for the postage of letters up to 20g within Europe. The current rate for that service is now 97p, so that's what each stamp is now worth.
Such stamps should be valid for postage within the UK but I wouldn't advise putting them on anything really urgent because the item might need to be withdrawn from the automated handling system at some point in its journey.