There is no doubt that the attitude and approach of a Prime Minister will affect, not merely reflect, the culture of those working around them and, ultimately, the country as a whole. That’s why an openly corrupt leader tends to preside over an increasingly openly corrupt establishment - he doesn’t come in with it all ready made and fully corrupted, he moulds it further to suit his needs.
We don’t need a report to know that Boris Johnson is a big drinker (he’s had publicised drunken rows with his now wife and, frankly, looks and sounds like a heavy drinker), so would no doubt have no problem with alcohol swilling about number 10. We also don’t need a report to know he wasn’t keen on his own covid rules and he made it clear from the start that he was personally happy to interpret them extremely flexibly, regardless of how confusing and difficult that made it for the police to enforce them, or the public to know whether or not they were on the right side of them unless they interpreted them as being very stringent. His entire modus operandi is to approach what others perceive to be strict rules and legally binding agreements as grey areas or irrelevancies that can be largely ignored when they are inconvenient. He made that approach clear with Brexit, let alone covid. Of course he knew at the time that others would think that what was going on was partying. He doesn’t really care. He’s not the one harmed by his liberal interpretation of the rules and guidelines, because he is in in the stratum of society that dictates to others, not the strata where others dictate to you, so he neither understands nor has any interest in those affected by his lack of comprehensible and consistent structure and guidance (ie leadership).