Ok, progress this evening:
UK17 (40ASA) shot as 3ASA, first dev is Rodinal 1+25, 20 deg C, 11 min, 10 or so agitations every minute, and the B&W negative got much denser, with lots of contrast. Then washed, stopped and exposed for about a minute 5cm from a 40W bulb, both sides. Then spooled and souped in diluted RA-4 dev until what I considering to be "completition", i.e. it didn't darken more. I removed it when it was completely black, then washed thoroughly and bleached. Then fixed in fresh C41 fix (from Digibase C41 kit).
The film is now much less dense, with saturated colours and distinguishable highlights, but no blacks, only greens instead of them. I guess either colour dev was insufficient, or exposure to light.
I'll be probably able to post a scan tomorrow.