Upload & Sell: Off
Hello WTP, and welcome
You could look at this site to check out the prices and, if you'd consider buying second hand you could look at MPB Photographic (I have bought from, and sold to, them and can recommend them) or Ffordes. There are others as well.
I've also recently bought a lens from ProCameraShop and they were fine, too. Great prices.
As for the retailers you list: I would happily buy from Amazon if the lens was being sold direct by Amazon but otherwise I tend to go direct to the retailer. Bristol Cameras have a good rep, as do Park Cameras, WEX (though sadly their prices aren't as competitive as they used to be) & Mifsuds. Not saying that the others don't, but I don't know anything about them. Well, apart from Jessops who can be hit and miss both on prices and service!
If there's a branch of London Camera Exchange near you, they'd also be worth a look for both new and second-hand.
You might have more luck asking about some of these on one of the UK-based photography forums.