Many expected the deal to go through, albeit with conditions. It didn't.
It's a story that has potentially huge repercussions for UK investors and Financial Planners too.
To quickly recap for those not too familiar with platforms: both FNZ and, to a large extent GBST, are platform 'engines.' They 'drive' or provide the crucial technology that runs investment platforms.
Most UK investors, if they use a fund supermarket, Financial Planner or adviser of some sort will have most of their assets held and managed on an FNZ or GBST-provided platform.
They are hugely important to the smooth running of UK platforms, most of which rely on these two companies.
About a year or so ago FNZ decided it wanted to buy GBST, its nearest rival. The move would undoubtedly lead to substantial consolidation but FNZ took a punt that the move would not be blocked. It was wrong.
The Competition and Markets Authority decided this week after a long investigation that the move was damaging to competition. It has not only blocked the move but also told FNZ to sell off GBST - a move I suspect produced howls in the boardroom.
The CMA was clear in its criticism. The move could substantially reduce competition, lead to poorer service and result in higher prices for potentially millions of investors, the CMA said.
The watchdog also hinted that FNZ should have thought about all this before going ahead with the move.
After a long and very complex investigation the CMA has probably come to the right conclusion.
Competition is key to keeping down or even reducing platform costs. Competition has already driven down platform costs significantly over the past few years to the long term benefit of investors.
Most Britons will not have clue about all this but the CMA could just have saved them an awful lot of money.
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Kevin O’Donnell is editor of Financial Planning Today and a financial journalist with 30 years experience. This topical comment on the Financial Planning news appears most weeks. Follow @FPT_Kevin