and a lot to be lost by openly opposing it.

That is the part I don't get. The default position of the opposition should be to oppose.

I accept that opposing "Brexit" had a lot of potential risks, but what he should have been doing from a fairly early stage was vehemently opposing a "tory-brexit". He could have peddled the line that a "good" brexit was possible (which he probably genuinely believes), while hammering the truth that the tories were royally screwing it up and were in fact using it as an opportunity to ransack the country and worsen the lot of the majority of the population. The only risk would have been if the tories did a good job, and if he still thought that was likely to happen after the first six months has passed, then he wasn't paying attention.