Not having seen the series for a few years, let me offer my perspective (as a 67 yo Brit with three grown sons) on British attitudes to sex - at the risk of vast oversimplification. First, there's a substantial difference between London English, other English and Welsh or Scottish approaches. Most of what you would see on UK TV generally reflects London English attitudes.
Like most things English, it is also bound up with the class system. Historically, the upper classes had arranged marriages and went at it like knives outside the marriage - once an heir and a spare were born. Anything went as long as it didn't become public. That of course altered with the advent of the tabloid and the paparazzi.
The working classes also went at it - in or out of marriage - with a lot of illegitimate births.
The middle classes sublimated their sexual needs - which leads to the stereotype of the repressed Englishman (see Baden Powell, Montgomery, etc.). The one place where they didn't sublimate was in the colonies - in fact, there's a school of thought that says that a lot of the motivation for people going to the Empire was to get their rocks off with the locals.
I think what you're seeing in the series is the repressed middle class Englishman struggling to come out of his shell in his mid-life crisis. It's exaggerated but not by much - and very funny. In my time, UK attitudes to sex have changed - I would personally say improved - substantially. While there's a lot of nonsense talked about the 60s, there's no question that, in Britain at least, it did free up an awful lot of those "hide it away" attitudes. Thank God!