So my new bb arrived, fitted it today, took the bike for a spin, and to my horror it was still creaking! Arrrgghhh. Still convinced it was coming from that area. Went and removed pedals and tried another set, still creaking, replaced pedals.
After fitting them I applied the brakes and stood in the cranks, and there was a creaky/click. So I knew (as suspected) it was something being caused by my pedalling force.
Then I had a thought, I bought wheels for the bike several months ago, they had an alu free wheel, the cassette had dug in to the spines, I wondered if that could be the source (hadn't even given it a thought). Removed the cassette, and some of the sprockets had dug in to the freehub, gave the cassette a good clean, replaced the cassette. I then noticed I was using a spacer between the wheel and cassette, and although it all fit, the spacer wasn't needed. Took it out, reassembled, and the free wheel was firm, tested it.... silence when pedalling.
So all solved, it was definitely something that got worse (i.e. no noise originally), but in hindsight either not fitted right (no need for spacer), or the cassette biting into the soft alu freehub and not sitting true or creating metal dust/debris.
So all solved and now with a different coloured and unneeded bottom bracket. Lesson learnt.