Since the merger of Orange and T-Mobile, EE have been cost cutting by shutting down cell towers with overlaps. This sounds reasonable, but it's having a huge effect on signal strength and quality.
Initially they denied there was a problem, now they can't hide the fact the service is suffering.
So if you're a business with £8 million in your pocket, make sure you do your due diligence and check coverage in your area! Remember what you check now might not be there when you want to use it, as EE are still decommissioning towers!