Around 15 years ago an MP stood up in Parliament and demanded to know why the new computer system for the Child Support Agency (CSA) was taking so long to be delivered.

The computer system was implementing the CSA’s ‘new rules’, which were being introduced to reduce the complexity of the calculation around how much the person paying the child support should pay. Under the new, simplified, scheme if you were paying support for one child then it would be 15% of your income, 20% if you were supporting two children and 25% for three or more children.

The MP – and I wish I could find a news story or a Hansard reference in order to name him – brandished a pocket calculator, such as you can buy for a couple of quid, and demanded to know why a sum that could be performed in seconds on a cheap calculator should be costing millions of pounds and taking years for an established IT consultancy firm to deliver in the form of a new computer system.

I remember it because, at the time, I was one of the many people working to deliver that computer system.

There are some complexities around the calculation itself; for example, the payment required couldn’t take the payee below the mandated level of protected income, but these were fairly trivial. Bigger issues revolved around actually determining a person’s income. For many of the CSA’s clients, working only in straightforward, pay-as-you-earn, employment, and those living on benefits, the calculation was, indeed, simple. Once you moved into the higher strata of society the problems multiplied. People went to enormous lengths to hide from the government how much money they had, solely in an effort to avoid paying for the upbringing of their own children. The CSA had specialist teams of people for dealing with self-employed absent parents, colloquially known as the ‘shoe-box team’, because of the frequency with which enquiries about how much a self-employed person earned were replied to with a shoe-box full of receipts and invoices, and a note reading, “You work it out”.

Above all of this the new system was a move away from the caseworker-centric model, where CSA employees had a stack of cases that were theirs, and towards more of a call-centre model. where if you needed a particular thing doing your work got somebody who could do that work, not just somebody who happened to be in arms-length of a filing cabinet with your paperwork in.

I could easily write 10,000 words about how complex that work-routing system was, because I was the person who designed it but, in brief, it had to understand things like the functional divisions within the agency, the regional divisions (sending a piece of legal work for someone living in Scotland to somebody used to working under English law would cause problems, for example), it had to understand there were times when people within the case couldn’t be made aware of who was dealing with it (if the case had been passed to the fraud team, say), it had to understand who could be trusted if a case about a premiership footballer, along with all of his contact and financial details, was flying around the system, it needed to understand that – while there’s no functional difference – there’s a material difference between dealing with somebody who wants to close her case because her and her partner have reconciled, and somebody who is closing her case because the child involved has died…

…but, more than anything else, the whole system needed to be able to withstand the unimaginable complexity of human life. The cases that you’d never dream existed – the man with 76 addresses, the man who was paying maintenance for his child, because he’d moved in with another woman, who was then claiming maintenance for her child, because she’d done a runner herself and left him holding the baby, the grandparents claiming against both parents, because they’d dumped the kids there one night for baby-sitting and then gone to start a new life.

That’s what takes the time. Not working out 15, 20 or 25% of an individual’s income, but spending hundreds of hours in meetings with people who knew what they wanted the system to do, or knew how the agency worked (rarely the same people), gaining the in-depth knowledge required to be able to explain it all to a computer algorithm.

Every large computer system is like this. Unless you’re an expert, or take the time to become an expert, then you have no idea how much work it will take. People in the forefront of political life are rarely experts, and never have the time to learn.

Don’t believe idiots waving calculators.