I've got a broadband cable running up to my home office which I would like to split into 2 so that one can go into my laptop (Wifi doesn't reach) and one into a Vodafone Sure Signal box (the one plugged in by the router downstairs also doesn't reach to the office). Is this possible? If so, how? Will I lose broadband speed if I do it?
Thanks

I take it you mean an ethernet cable? The easiest and best way to do this is a simple network switch. They can be very cheap like this

https://www.amazon.co.uk/TP-LINK-TL-...dp/B000FNFSPY/

https://www.amazon.co.uk/D-Link-Giga...dp/B008PC1FYK/

You plug the ethernet cable into one port and the remaining four ports can be used for whatever devices you need to connect to your router.

There are also versions with WiFi.

https://www.amazon.co.uk/Edimax-EW-7...dp/B004JV42A0/

This would allow you to effectively extend your WiFi coverage into the parts of the house the router doesn't cover. So you can also use devices that don't have a cable connection as well.

Actually this one -TP-LINK TL-SG105 5 port Steel Gigabit Switch (10/100/1000Mbps RJ45 ports although it costs a little bit more has gigabit ports which will serve you better for higher speed applications.