Thanks very much for that input.
I do not have an in depth knowledge of the intricacies of the QT wallet so I am confused to say the least.
When I used pywallet to dumpprivkey contents to wallet.txt, it gave about 200 addresses and keys. I only ever used the single address for transactions so perhaps some of those addresses listed are "change addresses" as previously pointed out by achow.
Now that I have the keys, I want to sweep them into my Electrum wallet so if I use Blockchain.info and identify all the change addresses from my transactions, I can cut and paste the privkeys from the wallet.txt file into Electrum for sweeping along with the key for what I consider as my main wallet address. I'll give it a go and see what happens

cheers,
kev