Thank you for your advice Gordon & everyone else who has contributed on this thread and others. I finally took the plunge today, made the call & once the advisor checked my records she confirmed that my pension was always dis-regarded under Invalidity and Incapacity benefits, so it's dis-regarded under ESA.
It was such a relief, even though I [knew/i] I should be okay, it's so difficult when those brown envelopes arrive. The advisor was amazed that this is the first time I've received one. She said they're computer generated. I wonder how much money they waste in postage, stationery and staff time every year?
Anyway, I just wanted to thank you all, I'm so glad I discovered this website in 2012. Annie:)
I've just received one of these letters for the first time & have been in receipt of IB/ESA since 1996, so the information here is very useful. Many thanks!