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Thanks - and thanks for the tip, although I wouldn't recommend any of these companies at the moment.
Without going into detail, Europcar charged me £187 without telling me (I found out by chance when I checked my credit card statement. £177 of this was supposed to be for bringing the car back a day late, when in fact I had returned it on time. Europcar shift responsibility to Car Hire 3000. Emails to Car Hire 3000 receive an automated reply that they will reply within 28 days.