@ Indrid
It was Nicholas and Julie / June. Australian cipher ex-girlfriend = Alison, hence cryptic crossword clue "she's all mixed up but the better part of Nicholas".
Now you mention it, the rumpy pumpy scene with the blonde goddess did indeed feel a bit crowbarred in. Ie you could skip it and it would all still work.
Apparently this is v noticeable in early 70s bookstand novels - a bit of explicit filth came to be expected. I've not read it but my brother tells me it's like this in Day of the Jackal where there are slotted-in scenes of lurve the plot doesn't need.
The worst thing about JF is the earnest 20somethings crapping on about how life's so like The Tempest and oh I must shag that old git.
Exactly how you think when you're 20 and locked into a cellar...
And he keeps using the word "guying" to mean "irritating" and affaire when he means "affair", though in fairness that's the arse narrator talking.