As all you old hands and legends will know, the Electrum Payment Slider offers three options: Static, ETA and Mempool. What are the pros and cons / advantages and disadvantages of each one. Unfortunately, I'm so green (although I am beginning to ripen slowly, thanks to you guys) that I don't even know what the Mempool is. Thanx   Amandrax

The transaction has NOT been confirmed, so the coins are not with the vendor.
NotATether was absolutely spot on-- I did indeed pay 1 satoshi/byte, so the 'stuck in the mempool' theory seems highly plausible.
I am happy to share the transaction ID, which is 3b15b25d0b3effadf66546e6f52934f4b03bd38c52b5c69137467d2b6c912155.

On 2nd December, I attempted a to make my first purchase with bitcoins from my electrum wallet. What I was did not know, was that the transaction HAD to be completed within one hour. Being a newbie, I set the transaction rate as low as possible (£0.02). And of course, the transaction was not completed within the hour. Thus, the vendor cancelled the transaction.
However, my electrum wallet shows the amount as having been paid, and has been deducted from my wallet. SO, where did my bitcoins go to (are they lost in cyberspace?) or will they be returned to my wallet in due course? In addition, the refund address that I generated has expired (Seven days is the maximum time that electrum allows an address to exist).