Country bumpkin here!
I have to come to waterloo station to make an Ebay pick up tommorow, I'm at UCL till 11am and will be heading out of town SW direction (towards kent!) So i cant park at UCL and tube there and back
Is there a short term car park at waterloo station i can use
If you have free parking available to you at UCL i don't think I see why you don't just park there in the morning, get the tube down to Waterloo to collect your ebay purchase (which will take about 15 minutes max on the Northern line - more like 10 on a good day), and get the tube back again. UCL is just as well placed as Waterloo for getting out of London.