What happens if I've (ok, stupidly!) placed an advance bid on item in eBay (with some in reserve) and also place a higher snipe bid?

Could I end up bidding against myself? Or does Myibay recognise that condition and withhold?

You can not bid against yourself.
Actually, eBay will recognize that and will not increase the current bid if you are the only winner there.

Thanks, and that sounds right of course.

Congrats on the v quick response time