Bitcoin following forks

[mpeill]

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?

[Bitfort]

Yes, your bitcoins are and will be valid. In addition your wallets now contain also BTG-bitcoingold and BCH-bitcoincash (if you held BTC at time of forks).

[mpeill]

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.

[Bitfort]

You have all three  
Try to check your BCH balace use e.g. https://bitinfocharts.com/bitcoin%20cash (enter your addy to see the balance). BTG is not yet fully ready as far as I know.

All are completely different coins (you can sell each of them individually) ... but problem is all coins are in the same address (so you need to extract them).
There is lot of guides how to extract BCH from your wallet (not yet proper guide how to do it with BTG). I used coinomi to get my BCH (sweep private key).

Just a hint: extraction ( in most cases) involves private key sweep so you should first send your BTC to new address and stop using the old one (it  becomes compromised).

[thedarksun]

Thank to that you have all three in one time in your wallet. So just take look at their prices, and you can sell them one by one.