OFCOM have a simple to use 4G mobile signal checker that enables you to insert your postcode and will then display that available service in your chosen location for the four main UK mobile phone networks.  You can view the 4G coverage maps for EE, Vodafone, O2 and Three mobile.  The Ofcom Sitefinder 4G signal checker will show the signal available for indoor and outdoor use as well as allow you to show the difference between voice and data mobile connectivity.