Don't think you can compare the Victoria line with Crossrail. The Victoria line is largely self contained and does not have to interface with all the differing signalling systems that Crossrail does.
In terms of Political interference, the decision to "Buy British" Bombardier trains when the project had already specified and bought the Siemens CBTC system has proved to be an absolute disaster. A lot on money has been, and is being, spent on engineering an interface between Bombardier and Siemens systems that would not have been necessary if compatible equipment had been purchased and with the various Networkrail signalling systems as Stratford and Paddington plus the Heathrow tunnels.
It is also worth remembering that Siemens had pulled out as they didn't have enough factory capacity to build the trains so Siemens trains weren't an option.
A few other bit relevant snipets on the signalling:
a) Siemens had only owned the former rail signalling division of Matra. It is effectively a Matra product not Siemens one, note the product name is Trainguard
MT, MT stands for Matra Technology.
b) Siemens have yet to build a train that uses TrainguardMT
c) TrainguardMT had only previously been installed on stand alone metro lines (e.g. Paris) or for heavy rail a maximum 16tph service level.
d) TrainguardMT then won 2 big contracts soon after being bought by Siemenss: Hong Kong (Central Link) and Crossrail, it needed significant functionality upgrades for both. It was sold as this
can do X, not
it already does X.
e) HK central link was meant to open 6months before Crossrail, it is now meant to open in "Spring 2021" and about £1.2bn over budget.
f) Crossrail is the first TrainguardMT installation where it is subservient to ETCS which now has to be the main on train signalling system for non standalone metros. This has been problematic to address.
g) after they had bid (and around the time they won) the CR signalling contract the same time Siemens bought Invensys would seem to have much more luck with ETCS interfaces (e.g Thameslink ATO). Most of the Trainguard MT issues are being sorted by what was Invensys (ex Westinghouse) in Chippenham as the ex Matra team near Paris didn't have the bandwidth to do so.
h) The CR CBTC signalling contract price was surprisingly low "less than £50m" (CR haven't disclosed the actual cost yet - search for contract C620). For comparison Thales on the Northern Line was £330m for the CBTC and SSR CBTC (3rd Attempt) £760m, (double the 2nd attempt cost). Siemens bid with TrainguardMT for Crossrail because it would provide a business reason to develop the additional functionality not already in the system and provide a reference case for other future project showing that it had been done. Basically a complex London or NY usage case are very useful for being able to handle anything elsewhere. The Crossrail contract price still appears very low compared to other recent London benchmarks.
i) on the SSR CBTC resignalling it is way behind on schedule and cost and may be descoped. Thales is having a bad time with 2 serious software related crash issues in Asia (HK and Singapore). It isn't just Siemens who have issues.
j) Siemens also won the related tunnel comms contract but also had lots of grief there as the leaky feeder cables weren't leaky enough, sorting this significantly delay the first trains running in the tunnels and hence delayed the discovery of many other issues.
k) for some parts of ETCS systems the UK has gone down a single supplier route hence Wabtec supply all the TPWS/AWS to ETCS computer interface modules. In a couple of other areas Bombardier decided it was cheaper to buy some other ETCS parts from Siemens than develop their own, but these come from yet another part of Siemens... Bombardier also use some of their own ETCS parts