Ah, see I'd understood that navigation lights were for making you visible (and I'm used to those from rowing on the Thames etc although have no intention of taking either flat bottomed boat there) but I wasn't sure what a tunnel light was.
The regs (9) made it sound like you had to be visible from the front (which makes sense) but @Scholar Gypsy implied they were for giving you visibility... In theory then I'd use both my white navigation light (of which I only need one, and at the front, for normal canal boating, no all-round requirement for ditch crawling) and also a tunnel light (optional) to help me see in a tunnel if I wanted.
Will have to have a play with the various white lights I have in the dark...
Also, am not wanting to take the p with an over stay. Had check with CRT about lights as was thinking would need to move boat in dark today after deliveries and they suggested better to overstay until daylight tomorrow. So, am free to move boat tomorrow at their suggestion, but that was made 4weeks or so ago when delivery was arranged and before such high winds forecast.