He is quoted on the Guido Fawkes site as saying that Tory voters are not so much “shy” as often “busy“ - e.g. harder for pollsters to get hard of because they are more often out (still at work, for instance.)
As the article on Guido's site continues:
"Curtice’s study found that if polls were based on people who answered the door on a first visit, Labour would be six points ahead. If polls were based on those who needed three to six visits before answering, the Tories had an 11 point lead. His conclusion: Labour voters were more likely to be at home rather than out at work.
“Conservatives are just simply more difficult to get hold of. There is an availability bias. People who you can get hold of first time round, who say, ‘oh yes come in’ are disproportionately Labour voters. The people you can easily get hold of are not representative.”As the old joke goes, the Tory voters really were still at work."…