4G Coverage Maps for the UK mobile networks can be found at the OFCOM website. You can enter your postcode and use the ofcom map as a 4G Signal Checker to work out if you will get a good or poor 4G signal indoors or outdoors.
The 4G signal checker provides information about the four main UK mobile networks, EE, Vodafone, O2 and Three mobile.
This information is only a guide and shows the availability of a signal only and will not provide any information or guarantees of service availability or 4G download and upload speeds.