Major issues from 2003-2006 are transmission. 3rd and 5th gear synchros killing themselves at no fault of the driver - this was a notorious issue that prompted nine (9!) different revisions for the Z's terrible 6-speed transmission - it was the prime reason my 350Z was an automatic, unfortunately (I really, really wanted a Z as you see). 2003 and 2004 models suffer from suspension geometry issues that can sometimes be hard to correct with just an alignment, and if not fixed properly by Nissan early on into the car's life, will cause enormous tire wear continuously. 05s and 06s with the "rev-up" motor (standard VQ35DE that revs to 7000RPM, 6-speed only) have notorious oil burning problems.
My suggestion? Find yourself that 2007 or 2008 with the slightly higher mileage. I beat the absolute piss out of my 2006 for 50K miles, and it never once gave me an issue. For the most part, Zs are extremely reliable - but without question the most reliable are definitely the later model cars. Avoid the 2003s-2005s because they are outdated, they have poor headlight visibility (the xenon projector is puny and not a real projector), the headlight is a little uglier on the inside, the taillights aren't LEDs and look very bland, the interior lacks certain improvements made for the 2006+ cars where the quality of plastics went up, and the amount of plastics used diminished. The standard brake rotors were made larger on 2006+ cars, and calipers were improved as well.
In UK you guys have the GT as the top of the line option, which offers the 18-inch lightweight Rays wheels.
Here's some I found, could be far from you, but I'm fairly certain they have navi despite the tiny pics.
http://www.autotrader.co.uk/search/...mission/manual/onesearchad/used,nearlynew,new
http://www.autotrader.co.uk/classif.../page/1/radius/200/postcode/se254aa?logcode=p
http://www.autotrader.co.uk/classif...red-listing/dealer/11913/usedcars?logcode=flp
http://www.autotrader.co.uk/classif.../page/1/radius/200/postcode/se254aa?logcode=p
Seems like the car is offered only Base and in GT over in England and most have Navi - which is opposite of American offerings. Get the GT, for sure.
Edit: You may know this, but seems like the model years in the UK are a little odd - but any 350Z with a hump on the bonnet means it is the VQ37 motor (to be 100% sure, check that the tach displays a redline of 7500RPM). If there is no hump on the bonnet, it is a VQ35DE. Seems like some 2007s in the UK still have the older motor - you'll notice that in the above links.