Waiting for your internet to be installed can be a massive pain. Fortunately, there are numerous options available to keep you connected in the short term.
If you have decent 4G or 5G signal, then you can use your smartphone's hotspot. Also known as tethering, this takes your mobile data and creates a mini-WiFi hub which you can connect other devices to.
Bear in mind that this will eat through your data pretty quickly, so make sure you have enough.
Another option is to invest in a dongle, which are available on contracts much like mobile devices. You select how many gigabytes you need and then plug it into your laptop. It will then use mobile data to provide a broadband connection for your device.
If these two options don’t work, then you can try to connect to BT’s WiFi, which allows you to pay for broadband services for a short time. This doesn't come cheap, however, and is only really feasible in a pinch.
If none of these work for you, then you will either need to find some publicly available WiFi or ask a friendly neighbour if they wouldn't mind you mooching off them for a bit while you wait for your installation.