Catherine MacLeod: A good 'spad' is trusted by the minister – and speaks for him

Being a special adviser at the heart of the Government is necessarily a privileged but hugely sensitive role. When Alistair Darling, then the new Chancellor of the Exchequer, asked me to be his special adviser in the Treasury in 2007 I had little idea of what was expected. There was no job description. It was a case of feeling my way, finding a modus operandi best suited to looking after his interests.

Absolute trust had to be at the heart of the relationship between us. I was his eyes and ears inside and outside the Treasury.

I was aware that anything I said could be attributed to the Chancellor, so freelancing was out. And while it is flattering to be called by some of the best known names in the land to reveal some policy detail or give a view on some political difficulty, any temptation had to be resisted.

Treasury officials handled the minutiae of policy while I handled the politics. That was a very important demarcation line. It protected civil servants from accusations of politicisation or the perception of such.

An effective special adviser has to be close to the Secretary of State and crucially has to be seen to be close. From day one, Alistair signalled strongly that I was to be trusted and could be party to sensitive policy discussions.

Civil servants are quick to note the relationship. There was not a day in the Treasury when I was not treated with respect. Quite often Alistair asked me to impart messages. There was never any doubt that when I spoke it was on the Chancellor's behalf.

The writer was a special adviser to the then Chancellor of the Exchequer Alistair Darling from 2007 to 2010