What camera do you have? A300?
I'd suggest skipping both of those lenses and instead try to find an old Minolta 70-210 f/4 Beercan or Minolta 75-300 "Big Beercan." Both are from the same first era of AF
glass and are quite good. Though they are used, you will be happy with their quality of build and optical quality too. Going prices for a used beercan are around $175 USD and a big beercan about $250. Not sure how that'd translate into pounds on eBay.
The el cheapo Sony 75-300 is actually the same lens as the Tamron 75-300. I'd avoid both.