Thank you, that's good to know. Where I now get confused is what I actually own..... perhaps I need to be pointed at a document that explains all this:
So, say I bought 1 BTC
After the forks, do I now have 1 BTC, 1 BTG and 1 BCH (as in, all three of them?)
When I sell, surely I can only sell it (them) once, so do I get the option of which coin type to sell.....what am I then selling?
In round figures:
1 BTC valued at £5000
1 BTG valued at £750
1 BCH valued at £400

What do I now have?
If I go to my exchange, presumably I can only exchange back the 1 BTC I originally purchased.

Another really basic question from a newbie...
After experimenting with small amounts, I purchased some BTC with the intent of just holding on to them over an extended time period, stored in several paper wallets, now sat in my filing cabinet.
I now read of various forks, including the Segwit2x later this month. So my question is, without really understanding the fork process, will my existing paper BTC wallets still be valid in several months/years time without the need to do anything, when I decide to exchange/sell these back to my local currency, GBP?

Sorted!
Evidentally I should have been using the "WIF compressed address", and not the "WIF address".
I'm not sure why, but, hey, it works!!

Ah, did it!! It's always the simple things. Thanks for your help.

The Private key started off life as encrypted BIP38, which I decrypted using the same bitaddress.org utility I'd used to originally create the paper wallet.
I am then trying to sweep the decrypted WIF private address 5K......

As a newbie, answering your last question first, I only deposited a small amount until I'm confident on the whole deposit to withdrawal mechanism, so no more deposits until it all works for me.
I created the paper wallet using bitaddress.org, offline, from a pc booted from a Ubuntu operating system on a usb stick.

Yes, I meant "Bitcoin address" where I deposited the bitcoin, starting 17P....

yes, I did use https://blockchain.info/address/17P....     (the same bitcoin address as above)

I used the same bitaddress.org utility using the Ubuntu booted pc to decrypt my Private Key 6P..... There didn't seem to be any issue there, and it gave me a WIF address of 5K...

It is showing as confirmed in blockchain.info

Doing an online check, my bitcoin wallet shows:

Total Received: 0.00296326

Total Sent: 0.00000000

Final Balance: 0.00296326

Total transactions: 1

So it does have a small value.

As a newbie, I'm trying to sweep my first paper wallet into Electrum, through the menu: Wallet / Private keys / sweep
I enter my private key 5Kj....etc, no spaces, checked the number numerous times, it is correct, but I just get the message:
No inputs found. (Note that inputs need to be confirmed)

What am I doing wrong? It must be something obvious!!

I've just created my first paper wallet, and purchased a small amount of bitcoin to test the process.
I first printed off securely a paper wallet, that provided a public and a BIP38 secured private key.
I then purchased the bitcoin mBTC and deposited that using the public key.
I checked that the bitcoin had arrived at my public key address.
I then tried to reverse the process, so first decrypted my private BIT38 key and found that the decrypted public key was different to the initial public key I had used for the deposit !
Is this normal? Can different public keys still point to the same private key?
If I then deposit more coins into the now different public key, will the deposit still end up in MY same wallet?