I fear this may be clutching at straws. BCG was used in the UK from 1953 and most children were vaccinated . So anyone born in the UK after ~ 1940 should be protected. But people in their 60s and 70s who should be protected by BCG are badly affected by the disease and many die. However, there may be two reasons for this. First, anecdotally, a significant proportion of those dying are from immigrant communities who may not have been vaccinated. Second BCG was not compulsory - my mum was an early anti-vac before anti-vac was invented and so I was not vaccinated until I was in my 20s. Let's hope...
Most countries vaccinate babies - often shortly after birth - but the UK vaccinated 12/13 hear olds from 1955 to 2005. So the oldest who could possibly have some protection would be 75 and the yongest 28. I don't know how quickly it was rolled out around the country. One issue would be whether there is a difference in effectiveness depending on the age of vaccination.
The countries whose BCG regime seems to have had the most impact on Covid 19 deaths are those that vaccinate at birth and follow up with a booster, and some revaccinate any who are not positive on the TST test. For example Hong Kong - 0.5 deaths per million, Singapore - 2 deaths per million, Japan - 2 deaths per million. Ant then there is Taiwan with 0.3 deaths per million who vaccinate at birth, age twelve and age 24!
Your second point about people from immigrant communities is more difficult as many of the countries they come from do have current ongoing vaccination programmes. But for example Pakistan introduced it at birth in 1978, So any Pakistani over 42 would likely not have had it. India vaccinated from birth from 1948. I don't know if anyone has done any analysis on the Pakistan/India breakdown of those affected in the UK.