Oh poor you, and on your first time ebaying too. Sod's law. I know how you feel, I have been unlucky enough to have dealt with 2 really nasty people before, and though I was really pleasant and fair(and not in the wrong may I add!), I still got bad feed back. Some people are just arseholes fullstop.
I think you should definitely try and get someone to go with you...anyone. But if all else fails then definitely somewhere very public.
What's his feedback like, that should give you a tiny insight as to what he has been like to deal with previously. Though don't take it as gospel!
Lisalisa, don't worry, he won't want you to leave him back feedback. Say you intend to pick the lego up like the email first said you could otherwise you will have to withdraw your offer. He'll soon sort himself out.
Maybe they were expecting more money for it so are being awkward?
If you really want it, insist that he sticks to his end of the bargain and lets you collect it as arranged from North London. Can't you arrange a meet-up with MNers so you have plenty of company to go along with
You don't have to worry about him leaving you bad feedback - because it's your first go on Ebay so you don't have a feedback record to lose. If he gives you bad feedback, you can just re-register on ebay with a new name and a new email address and start over. But he won't want you to give him bad feedback. So you're in a position to bargain. Or just to abandon it and not send any money if you want!