In movies and in fiction
That's where dramatization and fiction come into action. It reminds me the scene in Ron Howard's Inferno where Mr. Langdon's rental car is tracked real time.
That. Is. Drama.
In the real world (the "online world" is more real than we percieve), you should be aware that everything we do leaves traces. Traces that can be "traced back" using proper software. Real time is another thing.
There are multiple traces that you have done a transaction
'£88.50 at McGregor Inc., Snow Hill'. Especially at the bank issuing the credit card. We are now discussing whether it's possible or not to link those traces real time and who could.
In the financial world, there is not a single central database of transactions, but a multitude of entities have separate databases that don't all talk with the same interface, nor with a central authority, not real time. Even if the "three sisters" VISA MC and AMEX have a single huge database of transactions, they are three databases and you should be able to link these three. They are not banks, they provide routing to issuing banks, which provide authorization and settlement for transactions.
ACME Bank (issuing bank) and
McGregor Inc. (merchant, who owns a CRM software) have this record. Double linking all banks or merchants all around a country
is not possible. And let's see why.
Banks and regulators
In a number of countries, especially in EU (please add comments for US) banks are required to periodically report to Government agencies (e.g. IRS) about their customer and transactions. But 1) reports are aggregated and 2) they are periodic.
It means that there won't be a single State database where you can find
J. Smith purchased £88.50 at McGregor Inc.. And you (law enforcement) can access data only on a monthly/quarterly/yearly basis.
This because the privacy rules pose strong limits on what the self State.
The interesting part is that regulations are public and open, so before one claims "banks have a realtime link with MI-5", they would have to prove such a statement by linking appropriate regulations and practices.
About police/intelligence investigations
No law prohibits Law Enforcement and intelligence agencies to collect customer data on grounds of investigation. In EU at least, Law Enforcement can collect all information, including bank statements, on an individual basis. But that requires enquiring the Bank or the Merchant, which prevents realtime monitoring.
So that is where dramatization comes.
Oh, by the way, real world Law Enforcement require a warrant to obtain customer transactions. A warrant is issued in elapsed-seconds when watching a film, but can take much more time in the real world.
What it takes
In order to monitor one's transaction, authorities would have to establish a real time information link with all the appropriate parties.
For example a web service. A common interface to inquire all financial transactions in real time.
There are so many banks all around the world that if such a direct link existed secretly, there would be too many IT people involved in holding this secret.
I mean: either it exists, and is found online, a publicly accessible technical regulation from your Government, or it's a fake news. Reminds me that if Moon landing was a conspiracy, thousands of people should have been corrupted.
About different cards
They can likely be linked to you, simply by matching a unique identifier like you social security number, or tax identifier, as issued by the Government. Banks are required to verify, record and report the identity of their customers.
Note that I have been working for years in the RegTech industry. The Government could know how many cards (and where) you own, but not their PAN code.
Almost impossible. Impossible because banks have very sophisticated security systems, obey to strong privacy and security standards, and have plenties of people paid with a lot of money to protect their core systems.
Almost because sometimes, rarely, some bank gets hacked. But hacks don't last forever, and is for a single bank.
China is a different story. Chinese government is working hard to implement technology that allows to monitor society realtime, with obvious ethical, security and privacy implications which mark the strong cultural differences with Western society.
I have record (source: news) that Chinese government used big data from cell phone networks, face-scan cameras and AliPay payment network to track individuals suspected to have been in contact with COVID-19 patients. None of my sources mentioned
real time, though Chinese Government and technology firms are working towards that.