They are very strict in Newcastle now after years of bad press regarding underage drinking. You will get a different colour wristband to the over 18s but there are plenty of day events for the U18s. If you really are desperate, you can try and stitch together the tails of other people's wristbands and make your own! It's worked a few times before, believe me...
Fake IDs don't cut it anymore, your best bet is to try and use someone else's ID who looks similar to you, as someone who works on a bar I don't tend to look too closely at the photo, just the D.O.B.
That said, no harm in trying your luck...