Want something that is a good first bike and the missus will be comfortable riding.
Sorry but definitely a small engine for security..not over 250 cc..
I disagree. It's all about how you ride it -- if you're stupid on a 250cc you're going to get hurt just as much as on an SV650. The advantage of a bigger, but more lazy (torquey) engine like the SV's is that it's got enough power to get you out of trouble at most points in the rev range. So when you're still getting used to riding, if you get caught out in the wrong gear the bike will still pull reasonably well.
I wouldn't recommend a super sports 600, but stuff like the SV650 or "commuter twin" 500s are very common first big bikes here.
In fact if you want to do a direct access test (which gives you an unrestricted licence) you have to take the test on a bike producing at least 46 BHP, which usually means a 500cc. This is to prove you can handle a larger capacity bike, rather than passing on a 12 BHP 125cc and jumping onto a superbike.
I had an SV650S as my first bike, and it served me very well for a few years. Absolutely no regrets -- I'm sure if I'd gone for a 250cc I'd have been bored of it rather quickly.