Not only are there still some raves in some parts of the UK, the remaining big parties in other EU countries are very often not actually illegal. When/if they are they often get closed down very harshly with armed cops or in some cases gendarmes (paramiltary cops) using CS-gas and other nasty methods rarely used in the UK.
There is also as much surveillance on organisers, and penalties for organising an illegal event can be even harsher than UK because of a different legal system used in some EU nations where criminal and civil law is more strongly linked and a lack of a statute of limitations (so people can be, and sometimes are, busted for raves years after they happened!)
in reality most of the big Euro-events are tolerated by the authorities and the locals, often due to the organisers paying landowners for the use of the area and making sure at least basic health and safety procedures are present.
In some cases Councils actively assist people to put them on, even spending a certain amount of public money to do so.
In the whole EU we all have an overall right to free expression, balanced against others rights not to be distressed or inconvenienced by this (such as by noise, traffic or our public funded health services being overstretched by dealing with extra emergency incidents) – so any gathering (even in UK) only becomes illegal when it causes other people problems…
