Hi Nick,
The Spanish won't like your Aussie trailer and it would be a nightmare to get it approved. Chances are the drawbar, axle, lighting wouldn't meet the required standard anyway. If the trailer is older than Oct 2012 and you're towing it with a UK registered car the it would be ok to use but remember if you have any issues (breakdown, accident) with the UK car then you wouldn't be able to tow it with a hire car (and recovery vehicle couldn't tow it either) so you'd be looking at a low loader type recovery. Very happy to offer you more advise if you email me
marine@indespension.co.uk regards Jeremy