Could a new service from Clapham Junction to Blackfriars work

[Ianno87]

Clapham Junction to Blackfriars:
There are off-peak slots across Voltaire Road Junction at XX:04, XX:19, XX:34 and XX:49. That means departures from Clapham Junction at XX:13, XX:28, XX:43 and XX:58.
Brixton is passed 1 minute later, Canterbury Road Junction a minute after that, and Loughborough Junction 2 minutes after that (or at XX:08, XX:23, XX:38 and XX:53. There appear to be paths here.
Elephant & Castle departures are 4 minutes later at XX:12, XX:27, XX:42 and XX:57.
That gives an arrival time into Blackfriars at XX:02, XX:17, XX:32 and XX:47.
Journey Time: 19 minutes.

Blackfriars to Clapham Junction:
The off-peak slots across Voltaire Road Junction exist at XX:09, XX:24, XX:39 and XX:54, giving an arrival time at Clapham Junction at XX:01, XX:16, XX:31 and XX:46. I'll work backwards from here.
Loughborough Junction is passed 4 minutes earlier at XX:05, XX:20, XX:35 and XX:50. There are paths, although the XX:05 and XX:35 services are running parallel with services to Orpington from the Thameslink Core.
That means leaving Elephant & Castle at XX:01, XX:16, XX:31 and XX:46.
Thus, departures from Blackfriars are at XX:12, XX:27, XX:42 and XX:57.
Journey time: 19 minutes.

Problems:
Platforms at Clapham Junction for a start. Is constructing an additional platform worth it?
Will people use the service? It will basically run very slowly throughot (I can't see it breaking 30mph at all).
What about peak times? The slots across Voltaire Road Junction go, which either means a service with weird gaps or no service at all during peak hours, which is arguably when the service is required the most.
What about the additional stops (Wandsworth Road, Brixton, Loughborough Junction)?

Those Clapham-bound paths are exceedingly tight over Brixton Jn. There is 5 minutes between a Down Orpington stopper arriving at Brixton and the next Up Orpington stopper arriving at Brixton to sneak across the junction - the latter overlap locks up the junction so the headway is measured relative to the arrival, not the departure.

Not great to attempt 4 times an hour.

There is the small matter of platform capacity at Blackfriars too.

 

[swt_passenger]

I got the impression that there was a suggestion to extend some of the Southern London Bridge terminators on to Blackfriars. That couldn't be done at present, as there is no connection from the London Bridge lines into the bay platforms at Blackfriars. I assume that there must be a reason why a set of points cannot be installed on order to provide access to the bay platforms, as I can't imagine that this would not have otherwise been included in the Blackfriars remodelling a few years ago.

I think this has been confused in the past with the known plans to run Southern trains between London Bridge and Blackfriars via the Sutton and Wimbledon loop. I’ve been reading the relevant RUSs etc for years and a diversion of Southern trains from the London Bridge bays directly towards Blackfriars has never ever been mentioned.

 

[Bald Rick]

I assume that there must be a reason why a set of points cannot be installed on order to provide access to the bay platforms, as I can't imagine that this would not have otherwise been included in the Blackfriars remodelling a few years ago.

Not quite enough space, so some other and more useful facilities would have to have gone. Also, it would only ever be used if there was a problem in the TL core (or immediately north) and if so then the bays are needed for services from the Elephant direction. Meanwhile in the event of such problems, trains from London Bridge can turn back in P1/2 at Blackfriars or P4/5, 10-14 at London Bridge.