I don’t agree that the party of government should support the referendum result and the opposition not.
If they was the case the Tories should switch to opposing Brexit if they lost the election!
No I don’t think it is necessary for parties to hold an official position.
It’s easy for the smaller parties to take a strong position. If there was a referendum as at the link, then while the larger parties might adopt official positions, no doubt many within them would take a counter view.
At the EU elections, if you didn’t have a firm position on Brexit you were toast. It might not be quite so stark in a general election.
I have heard comments from several voters that they’re fed up with the main parties and are undecided on whether to vote Lib Dem or Brexit party however! A reminder that it’s not just the issue itself that influences some voters.