"NO RECEIPT openeth the heart but a true friend." Thus Francis Bacon in 1625 articulated the phenomenon which nowadays goes by the description "bromance". In the Protestant early modern world, the bond between man and man was seen to replace the emotional prop provided by the RC priest. As Bacon puts it, a Renaissance man can offload to a buddy "whatsoever lieth upon the heart to oppress it, in a kind civil shrift or confession".

In modern-day bromance, this civil shrift might take the form of six pints and a late-night confession that your companion is your best mate ever; but the principle is the same. It is the love of David for Jonathan, reinvented every night as young men totter towards bus shelters or taxis. Then it is back home for a late-night session in front of the computer, and an ill-thought-out rant on Facebook.

Thomas Dixon's excellent Five Hundred Years of Friendship (Radio 4, weekdays) has brought us so far only to the end of the 18th century - though the era of social networking is on the horizon.

We heard of models of friendship established in the classical mould by the likes of Erasmus and Thomas More. But the most powerful examples are set by female relationships, such as that of the Quakers Katherine Evans and Sarah Cheevers, whose incarceration by the Maltese inquisition, in the 17th century, provided the Society of Friends with a prototype of friendship in hard times.

This was a time when our circle of friends would consist largely of those we had some kinship with - unlike today, when we count as friends only those to whom we are not compelled to be civil at family get-togethers. The anthropologist Robin Dunbar says that ourbrain-capacity prevents our having meaningful relationships with more than about 150 people. This may seem limiting to some, but a considerable challenge to others.

Fictional friends do not count, although our relationship with a character from a soap opera or sitcom might appear more meaningful than many of the real human interactions we have. This sense of affiliation with the fictional was the premise behind Radio 4's Character Invasion day last Saturday, when schedules were interrupted by guest appearances by fictional celebrities.

Lynda Snell, from The Archers, phoned Any Answers with a question about parish councils; Tweet of the Day featured Big Bird, from Sesame Street; and Francis Urquhart, from House of Cards, revealed his morbid "inheritance tracks" on Saturday Live.

What with the spoof documentary W1A currently running on BBC2, there is quite enough self-referential comedy going on on the BBC at the moment; and this project looked like something that might have started as an April Fool's Day idea before somebody got carried away and decided to make a day of it.

Most effective was Garry Richardson's interview on Today with Roy of the Rovers. "It's funny not seeing your voice coming out in a bubble," quipped the star of Melchester Rovers. Most cringe-worthy was the Vicar of Dibley segment, which used Third World poverty as a foil for the Vicar's trite quips. Another reminder of how much better off we are with Rev.