I've got a work experience week/two weeks next spring at UBS. I don't know how much it will/has help me/my application, but it's no doubt better than nothing. But I think Paul is right, it's more important to read some decent economics books - takes you away from the dullness of A-Level Economics, and visit some countries that are interesting economically (i.e. are rapidly growing). I'm going to Eastern and Central Europe next July (assuming I earn enough) for this very reason.
If you did want work experience living in Northern England may be a bit tricky, simply because most of the relavent firms are gathered around London - though I don't really know.