This is highly likely to be a localised issue, although there's a popular misconception that "only 1 bar" is automatically a bad thing and the cause of poor data speeds or call quality when that's not necessarily the case.
In the first instance, use the online coverage tool at https://ee.co.uk/help/mobile-coverage-checker to "check service status" and then "report a problem" if one's not already listed.
For the sake of testing, check whether you are able to make & receive calls OK - this is a good test of whether you fundamentally have network coverage and this is potentially just an issue of data speeds.
