How can I get internet when my WiFi is down?

The following solution will use your mobile phone's data. Please be aware that data charges may apply.
Wi-Fi down
We've all been there..... you're rushing to finish off that piece of work you promised would be ready for the morning, or you're engrossed in the latest blockbuster movie when...... boom, your internet goes down and shows no sign of coming back any time soon.
You've reset the wireless router. You've checked all the connections. The lights are on, but nobody's home.
Panic ensues. Your blood pressure starts going through the roof with frustration...
What do you do?
How to get your devices back online when you have no WiFi
If you're in a situation where your mobile phone is the only thing that's working, and all of your other devices are offline because they have no internet connection, it may make sense to use this nifty trick. All you need to do is set up an ad-hoc wireless network on your smartphone using its Hotspot feature. This will allow any device connected wirelessly with Wi-Fi enabled (including laptop computers) at the same time as by connecting via USB cable or Bluetooth - even if those wired connections fail!
Your devices are already configured to connect to your wireless router using the SSID (your wireless network name) which is usually something along the lines of BTBHub6-abdk3 (we're using a BT Internet in this example) and password.
You can find the SSID of your network on a label, either underneath or on the back of your router -

Make a note of your SSID as you will need this for the next step (be careful to note it down exactly as it is written on the router, as SSIDs are case sensitive).

For BT Internet users the label will look like this -
For those with an Android phone -

Go to the Mobile / Wi-Fi Hotspot settings on your Android smartphone. You will see a screen that looks something like this -
Click 'Details' > 'Configure'
Rename the Network Name field to match your router's SSID, and the Password field to match your router's password.
Bingo! Your devices will now think your smartphone is the router and will use its connection to come back online.
For those with an iPhone -

For iPhone it is a little more complicated, but will still work.
Go to 'Settings' > 'General' > 'About' > 'Name'
This will usually say something like [your name]'s iPhone -
Change this to the SSID of your router. Once this is done head back to your main 'Settings' page and tap on 'Personal Hotspot'.

Tap on 'Allow Others To Join' to allow your devices to connect.
Below that, change 'Wi-Fi Password' to match the password of your router.
A little more complicated but, just as with the hotspot on an Android phone, your devices will believe the iPhone is your Wi-Fi router and will come back online.
Finally, to avoid any interference, you may wish to turn off your wireless router.
Provided your smartphone is receiving a decent data signal, all your devices will be back online.
What happens when the broadband connection comes back online?
When your broadband internet signal comes back online make sure your wireless router is turned on and all lights are illuminated.
Next, simply turn off your smartphone's Hotspot and all devices will automatically reconnect to your wireless router.
.....You're welcome!