Thanks everyone. It had a Race Face BB in it. The bearings were rubbish and I had them replaced many times. In the end I decided to run them until absolutely finished and then throw out the RF BB and start again with a Hope.
I knew I wouldn't be able to get the old BB out so I took my bike to a shop, with the new Hope BB (in its packet, with the instructions) and asked them to get the old BB out, chase the threads out and face the cups.
When I picked it up they had (apparently) done all that, plus fitted the BB, which I had not asked them to do. I just gave it to them so that they could see if they had chased the threads out properly.
There was another issue, but never mind about that for now.
I rode my beloved for a bit, then decided to change the chainrings (plus chain and freewheel). When I put the chainset back on I thought it was funny because I could either tighten it until tight and the BB made a little whooshing noise, or I could back off the crank bolt and the bearings did not make the noise. I was riding another bike anyway so didn't think about it too much.
Any road up… sorry about the length of this post – yesterday I just had to ride my 5. I got maybe 1km down the bridleway next to my home and the cranks were loose. Went home, got an allen key, tightened until I could spin cranks without the little whooshing noise. They came loose again, and again, so I went home and posted on here to ask you guys what the hell is going on?
The shop have put two spacers on the non-drive side and they have probably overloaded the bearings. Wonder if that means the bearings have had it? They are the ceramic ones 🙁