The Silver Cross 3D is rubbish to be honest. If you search through this section you'll find loads of threads from people who bought a 3D and are desperate to swap it by 6 months. It seems like the ZeZu is a reasonable pushchair, but doesn't necessarily have the quality to last a long time.
If you're happy to go forward facing from 6 months, the ones Tiggy suggested are definitely what you should be considering.
Otherwise, the BabyStyle Oyster is good as long as your child isn't likely to be too tall. Just make sure you pay the extra £25 for air tyres as they make a big difference to the ease of push and suspension.
Are you willing to buy second hand? If so, there are lots more you will find at the same price as a new ZeZu or 3D. For example, a Bugaboo Bee (but check the wheels, handle extension and turning the seat around as these are all known issues), Jané Rider, Seed Pli (this looks big but is actually only 59cm wide, but has a very tall seat), Bugaboo Cameleon/Gecko/Frog, Silver Cross Surf, Joolz Day.