Having worked along side a number of government projects, I can confidently say that all the projects based on "off the shelf" products end up becoming vastly more expensive because you usually end up with hugely expensive support contracts with BT / IBM / MS / Oracle / etc and often the solutions need some bespoke tuning to work the way needed, so you add on expensive consultancy costs to have the software adapted to fit.
Where as developing stuff in house means that you're employing significantly cheaper labour (namely, the rubbish salaries that most get in the public sector vs the private sector) and as a bonus the cost is more likely going to stay within the UK (ie you're not paying multinational companies nor their overseas consultants (Oracle was particularly bad for this as they dumped our stuff in a US data centre and our support contacts were all living somewhere in eastern Europe. So very little - if anything - provided was UK based).
Sadly our government doesn't seem to understand about doing anything in between - or at least not that I observed when I used to work there. It was either entirely bespoke or entirely bought, developed and set up by some overpriced conglomerate (or worse yet, outsourced completely). So going by the trends that I've witnessed, I'd rather the technology playgrounds just so long as they remain developed in house.