Assuming your on one ticket there's no real risk really although flights in any airport can be delayed etc for a variety of reasons. At LHR it is usually weather if anything why flights can be delayed but it's not that often really. BA will look after you if you did miss your connection for any reason.

As an example KARFA (and some others too) travel numerous times through every week through LHR T5 and no major issues really as posted here. BA have loads of flights coming in and out every day, usually over 300 departures, and the vast vast majority of connecting passengers have no issues.

https://www.flyertalk.com/forum/36042285-post1046.html