So here's my hypothesis as to what happened.
SJL slept with others while she was with AL, including while he was on holiday. When he got back, instead of the expected ecstatic reunion sex he was looking forward to on the Friday, she blanked him. He did not see her on Friday, nor on the Saturday (when she possibly copped off with someone else), nor on Sunday when she went to the coast (he followed) and back (he followed) without him. This is not how you conduct yourself towards your sole bloke whom you've not seen for 2 weeks. He got the firm elbow on Sunday evening at the PoW, after she had pointedly ignored him all weekend.
Her anxiety to get the diary back was because if the pub somehow had it, it meant AL did not, as it contained stuff she did not need him to know. The items were lost there on the Sunday, not Friday, otherwise it could not have been CV who found it.
AL's self-contradictory accounts of the last weekend (telling a TV doc he and SJL went to the PoW on Friday, telling DV he'd never been there) were to save face; to suggest that he and SJL were still a thing (a recent split would be troublesome to explain to LE given she had just disappeared); and fortuitously, to support the impression of SJL that also happened to suit DL.
On Monday SJL initially arranged to go to the PoW after work. Then a 6pm second-viewing request came in. This was more important, so she rang the pub back and postponed the pickup to just "later". CV's recollections a year later of calls to the pub that afternoon are misrecollections of various conversations he had the following day.
When she left the office, she did not go to 37SR. No trace of her (e.g. her fingerprints) has been confirmed to have been found there. If she went inside with her killer, he could perhaps have avoided touching anything, but someone had to open doors and touch handles and switches. There's no sign she did.
So, as she never went inside 37SR, the woman exiting it via the front door whom HR saw cannot have been her. That identification, and the other "sightings" of her there, originated entirely with the police, or with people coached via TV to echo the police account. HR actually saw SF and MG, who went in and out some hours later, using the keys that SJL did not take. Although he never claimed he had seen SJL, HR's grossly misleading account provided him with years of excitement and attention, provided it kept changing according to what he was being asked to confirm. So the good-looking late-20s Mr Kipper he first described became a podgy 44-year-old Belgian diamond dealer when HR was later shown a photo of one. The sketch of "Mr Kipper" is most likely just a generic 80s yuppie estate agent, such as her boss.
Instead, she went elsewhere by arrangement, with someone she knew (i.e. the BW sighting in FPR is quite likely correct). She was led inside a nearby property - perhaps on the pretence that a sale instruction might be up for grabs - where she was attacked and at some point killed.
The property was one of which the killer had free run - a rented house or ground-floor flat, perhaps abutting waste ground; maybe a house the killer had bought and was converting into flats. The killer next ditched her car at about 4pm; the sightings of her car outside 123SR before then are all spurious. He then went back to that property. She may still have been alive at this point. She is probably under a floor or a patio somewhere in west London; Ladbroke Grove, Shepherds Bush - somewhere like that. If you take up the floorboards of a house built 100 years or more ago, you will find a space under the floor, and then the dirt it was built on, a couple of feet below. Some such houses have hatches let into the floor so you can inspect water pipes etc underneath without taking up the floor.
The property passed soon after into others' hands, its condition unremarkable. The current occupants know nothing.
The initial police inquiry failed because it focused on identifying everyone SJL knew who was in Fulham that afternoon. This did not work for three simple reasons. One, they did not remotely identify everyone she knew, due to how she compartmentalised her acquaintances. Two, she herself wasn't in Fulham that afternoon. Three, they had asserted - in advance of knowing the facts - that she went to Shorrolds. Consequently, anyone who might have thought they had seen her anywhere else would have been put off reporting this, because it couldn't have been her.
The second inquiry failed because its ToR were to implicate or exonerate Cannan, to which end JD solicited sightings by the public of Cannan, fourteen years ex post. Its approach was to repeat the previous investigation, with Cannan lobbed in as a suspect. Once it reached the same conclusion about everyone in Fulham as the first investigation, and having prompted a lot of spurious coached "sightings" of Cannan, that only left Cannan, so QED; he must have done it. This, of course, fails the Ronald McDonald test (but is consistent with contemporary police procedure, e.g. Rachel Nickell, Jill Dando). Cannan had nothing to do with it, which is why zero evidence against him has ever emerged.
I have no idea who the killer was. It was someone she knew well enough to go off with alone, who had access to empty property she would enter without demur, who needed to kill her, and who he knew in advance he was going to do so and planned accordingly. The motive for killing her could be her knowledge of some sort of property fraud; his jealousy of not being the only man she was sleeping with; rage at the money she'd cost him by welshing on a deal (if there's a TS connection); or simply a need to avoid prosecution after raping her.
Purely MOO but aligns with or explains pretty well all the known facts...
