It happened at a government dinner party in the Belfast Europa Hotel in 1978. As the 20-or-so guests stopped their conversations to listen, Roberts described our private phone exchange in embarrassing detail.

I had been the Guardian's Northern Ireland correspondent for two years and Terry, my boyfriend of 18 months, was a teacher in London. We were about to get married and there was tension in the air. Our row had started about trivia - whether he or I had left the freezer unplugged last time I was in London - but moved on to an angry debate about how long I would continue to work in Belfast. It was a disagreement any couple would recognise, but certainly not something anyone would want aired at a working dinner with strangers. Thirty years on I am still outraged.

Roberts, who died a decade ago, was a hard-drinking former journalist in his 50s, who was also a colonel in the part-time Ulster Defence Regiment. He had been drinking whiskey all day. Another press officer, Fred Corbett, said he wanted me to sit by Roberts since "you might be able to persuade him to eat something". Roberts, glass in hand, refused to eat. He talked about the UDR. Then he leaned towards me. "That boyfriend of yours doesn't like you being here," he said.

It felt like a tape had started playing in my head. I knew I hadn't described that conversation to anyone, and there was only one way Roberts could have known. "Where did you hear that?" I asked, seeing Corbett turn ashen. "On the tapes," Roberts replied aggressively. "The secretary of state and I were listening to the tapes!" He went on to berate me for being too pro-Republican and claimed that drastic measures to get rid of me had been considered, including planting bullets in my handbag to perhaps get me prosecuted.

All journalists working in Belfast were aware that our phones were almost certainly tapped. I also knew that phone-tapping was legal only if it had been authorised by the secretary of state and that phone taps could not be used to gather personal information, but only when security breaches or criminal activity was suspected. And I had heard the repeated Northern Ireland Office denials that tapping was used on journalists or politicians.

But being aware was no preparation for the shock I felt when Roberts started talking. To this day I remain cautious on the phone - and I have always felt sceptical whenever government ministers pipe up to protest their innocence in bugging scandals.