That would provoke a constitutional crisis and, very possibly, an immediate second election. (yougov.co.uk)
He might not be able to carry his MPs with him, which might lead to an earlier second election (and possibly an implosion in the Lib Dems). (liberalconspiracy.org)
Moreover, as John Curtice shows [Nuffield appendix], the political geography of the UK has changed in recent years, producing fewer marginal seats and so making a victorious second election even less likely. (newstatesman.com)