Abellio London may have a unit for TfL work but it does not operate any duties for their TOCs.
They have done so in the past. The TfL rail replacement work they do the bulk of is their forte. The same model of operating was copied to the TOC work - use of buses limited to 30mph, drivers travelling across London to/from Newbury Park by public transport for shift changeovers to take over hybrid buses with a 320 mile fuel range covering 350+ mile running boards. These jobs haven't been covered for a few years now, the focus is now kept on rail replacement for TfL.
In addition to some service drivers doing rail replacement on rest days, they make use of an agency for drivers, consisting of a percentage of regular drivers and a percentage who come and go. They provide comprehensive training material for route learning, requiring drivers to sign a declaration saying they have studied them prior to the shift. Drivers are supported by route pilots where necessary and routes are signposted.
Some companies set up operating units using cascaded vehicles. London General Commercial Services is one. As mentioned, they have outposts around the TSGN fracnchise area.
In addition, Go-Ahead London have two panels for rail replacement - Commercial Rail Replacement and Commercial Private Hire who operate quite differently. The former consists of quite the army of dedicated rail replacement drivers who declare availability the previous month and receive duties in the post every week. It is run very well and the drivers are very well aware of what's expected of them. Drivers pick which of the London depots they are based at and the nature of the job means the routes are sometimes quite distant from the depot. Usually they're given a bus by the engineers and off they go. As a Morden Wharf (Greenwich) based driver, the majority of the time I did SE London/North Kent/Sevenoaks area stuff, the Bexleyheath and Croydon based drivers were more likely to be sent to the coast.
How does that work if they need to source RRBs for the GWML? Do the TfL buses come all the way out to Reading?
TfL usually cover the service out to Slough. In the past I've done it as far as Maidenhead under Abellio London for TfL but I'm not sure if they've ever covered as far as Reading.
Unlike most operators, emergency rail replacement is a significant part of the Ensign business. As it is very difficult for other operators to cover emergency jobs, Ensign do a lot of it - anywhere up to 100 miles away from base. I think it must be quite profitable - and, they make it quite profitable for the drivers too. To answer the question above, First Travel Solutions currently has no involvement withc2c rail replacement.
I run an operation which is specifically set up to respond to emergency rail replacement calls and I'll often take on and cover several jobs in one go.
It is of course contingent on the rate offered - my buses frequently cover e-rail jobs 250 miles away. My phone is available 24/7 and I'll happily assist if I have the resource spare. However there are times when I'm unable to accept closer e-rail jobs. The truth is, in response to dropping everything and dispatching a vehicle immediately, the emergency rates offered by some do not cover the operational costs of sending the bus out, let alone a contribution to the overheads pot or profit.
The reason some operators say yes to those rates is the bus is already out working and broken even for the day so the wage costs are marginal.
Down here in Sussex the only company that seems to run emergency rail replacements is actually Ensignbus, the 2 times i've seen E-rail replacement at East Grinstead on both occasions it has been Ensignbus vehicles that have turned out. On planned stuff Go-Ahead London seem to operate a lot of services and i'm seeing less coach operators turning out recently, although admittedly I haven't seen rail replacements around as often. I've only seen minibuses turn-up a few times, twice on East Grinstead-Oxted stoppers and once on a Three Bridges-Lewes run of all things.
I go out and do the e-rail jobs in Sussex sometimes, I have depots in South East London and Sussex I can dispatch vehicles from.