This is the policy of
http://www.fastcarhire.co.uk/Can collect from most of the airports it seems, but there also appear to be a minimum of three day hire for some places.
Cars may be driven free of charge into Austria , Belgium, Denmark, France , Germany Italy, Portugal, Leichtenstein, Luxembourg, Spain, Netherlands, Scandanavia, Switzerland Portugal, UK, Rep of Ireland, and Denmark.
Cars CAN be driven into these former Eastern Europe countries, Hungary, Slovak & Czech Republic, Slovenia & Croatia, but local surcharge of €10/day + VAT applied for full duration of car hire rental, and not for days spent in Eastern Europe.
Car CANNOT be driven into Russia, Poland, Romania, Bulgaria, Greece, Turkey and former Yugoslavia. Please advise if paln to visit other countries as this is not a definitive list