I just want to buy £50 worth and forget about it for ten years. I live in the UK, don't have a smartphone, bank online, but can't prove ID easily (because I rent a room in a block). I don't understand highly technical explanations. What's the best wallet for me?
When you register to LocalBitcoins you get a free web bitcoin wallet. You can access this with a web browser and protect it with secure paper codes log in.
Also the site allows you to buy bitcoins with cash, so you get two birds with one stone.
Use Coinbase or Localbitcoins, more preferably localbitcoins as coinbase has some anti-consumer tactics to get them profit. They mark transactions as "suspicious" 5 days later when bitcoin gains price and process transactions when the price of bitcoin falls, essentially using the customer as an entity that inherits all risk in trading. Be careful with localbitcoin too, use escrow and if you are meeting the person physically make sure it's in a public place like a coffee shop.
To robustly store bitcoins, get electrum. Write down the seed it gives you when you first make a wallet and make sure you use it with a password. For extra precaution export the wallet onto a usb and if you use a good password you can also just leave a copy of the encrypted wallet on google drive or other computers. This is safe to do as a passworded wallet is encrypted. You can go for a "paper wallet" if you are even more paranoid.
10 years is a long time, in that time there is a small but not none chance that Bitcoin's cryptographic algorithm may become weak. If your £50 turns into a sizeable amount you will need to be up to date on bitcoin news, don't be those people who are digging through waste dumps for a hard drive full of 10,000 bitcoins.
Please do not use a web wallet if you are planning on sitting on your coins for 10 years. When you send coins to a web wallet or to any address you did not generate yourself, you are giving the spending power to another person. Just like when you deposit $100 in the bank they will use it for other things and in most certainty return you a different $100 should you go and withdraw it.
Download the original bitcoin-qt client and open it, it will begin to download blocks, but this is not important if you are planning on just sitting on your coin. On the first run the client will also generate some addresses for you, showing you the first one on the "Receive" tab. You can have your newly purchased coins sent to this address.
There are plenty of security steps to safeguard against loss, please read carefully and understand that if you lose access to your coins or if a mischievous person gains access to them, they will likely be gone forever.
It is strongly recommended you encrypt your wallet asap. Please pick a very long passphrase you can remember, at least 6 to 8 words. Be aware that forgetting this passphrase will likely result in the permanent loss of your coins (there is no "Forgot Password" option). If you have strongly encrypted your wallet, then it is pretty safe to put it in as many places as you can, since cracking a random 6 to 8 word password would take an unreasonably long time using traditional password cracking methods.
You can find your wallet file on windows by opening the file explorer and typing %appdata% in the path (where you usually see c:\user\documents, etc), then selecting the folder named "Bitcoin". Inside this folder you will see a file called wallet.dat, this file can be placed in this folder on any other computer, giving this computer the ability to see and spend the coin associated with address on this wallet.
Should you decide not to encrypt your wallet, you can still copy it to a USB and put it in a safety deposit box, or somewhere else secure, but please be aware that any person who has access to an unencrypted wallet.dat can easily load it to their computer and send your bitcoin off into cyber-space.