Usually one of your choice if that's within reasonable distance (i.e. it costs no more than EUR 200 to tow your car to that particular garage). It really is explained on this page (blue_hubbas link)

ADAC is quite popular in the UK now, as the "Plus" membership is much cheaper than any of the UK breakdown assistance deals (AA, RAC,...), but includes Europe, and even some (limited) worldwide assistance. Last time we called the ADAC to get our car going (was parked in front of the house - yep, home start is included) they sent an AA van. The driver said he'd seen a lot of UK registered cars with UK owners where the owners relied on ADAC membership for breakdown assistance. He then asked us for the link to the membership application, as ADAC plus membership was cheaper for him than the AA package, even allowing for his employee discount (!).